diff --git a/core/src/mindustry/content/Blocks.java b/core/src/mindustry/content/Blocks.java
index 6226dbae5d..b3ff2389c2 100644
--- a/core/src/mindustry/content/Blocks.java
+++ b/core/src/mindustry/content/Blocks.java
@@ -1350,17 +1350,20 @@ public class Blocks implements ContentList{
             requirements(Category.effect, with(Items.titanium, 250, Items.thorium, 125));
             size = 3;
             itemCapacity = 1000;
+            group = BlockGroup.storage;
         }};
 
         container = new StorageBlock("container"){{
             requirements(Category.effect, with(Items.titanium, 100));
             size = 2;
             itemCapacity = 300;
+            group = BlockGroup.storage;
         }};
 
         unloader = new Unloader("unloader"){{
             requirements(Category.effect, with(Items.titanium, 25, Items.silicon, 30));
             speed = 6f;
+            group = BlockGroup.transportation;
         }};
 
         //endregion
diff --git a/core/src/mindustry/entities/bullet/BulletType.java b/core/src/mindustry/entities/bullet/BulletType.java
index bd4d57c771..e748310b8a 100644
--- a/core/src/mindustry/entities/bullet/BulletType.java
+++ b/core/src/mindustry/entities/bullet/BulletType.java
@@ -85,7 +85,7 @@ public abstract class BulletType extends Content{
     public float fragAngle = 0f;
     public int fragBullets = 9;
     public float fragVelocityMin = 0.2f, fragVelocityMax = 1f, fragLifeMin = 1f, fragLifeMax = 1f;
-    public BulletType fragBullet = null;
+    public @Nullable BulletType fragBullet = null;
     public Color hitColor = Color.white;
 
     public Color trailColor = Pal.missileYellowBack;
diff --git a/core/src/mindustry/entities/comp/BuildingComp.java b/core/src/mindustry/entities/comp/BuildingComp.java
index 540392c743..bf4236ce53 100644
--- a/core/src/mindustry/entities/comp/BuildingComp.java
+++ b/core/src/mindustry/entities/comp/BuildingComp.java
@@ -849,6 +849,13 @@ abstract class BuildingComp implements Posc, Teamc, Healthc, Buildingc, Timerc,
         }
     }
 
+    /**
+     * Called when a block is placed over some other blocks. This seq will always have at least one item.
+     * Should load some previous state, if necessary. */
+    public void overwrote(Seq<Building> previous){
+
+    }
+
     public void onRemoved(){
     }
 
diff --git a/core/src/mindustry/world/Block.java b/core/src/mindustry/world/Block.java
index c7b07fe401..7fe708ce7d 100644
--- a/core/src/mindustry/world/Block.java
+++ b/core/src/mindustry/world/Block.java
@@ -198,6 +198,8 @@ public class Block extends UnlockableContent{
     public boolean instantTransfer = false;
     /** Whether you can rotate this block with Keybind rotateplaced + Scroll Wheel. */
     public boolean quickRotate = true;
+    /** Main subclass. Non-anonymous. */
+    public @Nullable Class<?> subclass;
 
     public Prov<Building> buildType = null; //initialized later
     public ObjectMap<Class<?>, Cons2> configurations = new ObjectMap<>();
@@ -371,7 +373,7 @@ public class Block extends UnlockableContent{
 
     public boolean canReplace(Block other){
         if(other.alwaysReplace) return true;
-        return (other != this || rotate) && this.group != BlockGroup.none && other.group == this.group && size == other.size;
+        return (other != this || rotate) && this.group != BlockGroup.none && other.group == this.group && (size == other.size || (size >= other.size && subclass != null && subclass == other.subclass));
     }
 
     /** @return a possible replacement for this block when placed in a line by the player. */
@@ -590,6 +592,8 @@ public class Block extends UnlockableContent{
                 current = current.getSuperclass();
             }
 
+            subclass = current;
+
             while(buildType == null && Block.class.isAssignableFrom(current)){
                 //first class that is subclass of Building
                 Class<?> type = Structs.find(current.getDeclaredClasses(), t -> Building.class.isAssignableFrom(t) && !t.isInterface());
diff --git a/core/src/mindustry/world/Build.java b/core/src/mindustry/world/Build.java
index 15c7decbcf..070ddab553 100644
--- a/core/src/mindustry/world/Build.java
+++ b/core/src/mindustry/world/Build.java
@@ -3,18 +3,21 @@ package mindustry.world;
 import arc.*;
 import arc.math.*;
 import arc.math.geom.*;
+import arc.struct.*;
 import arc.util.*;
 import mindustry.annotations.Annotations.*;
 import mindustry.content.*;
 import mindustry.entities.*;
 import mindustry.game.EventType.*;
 import mindustry.game.*;
+import mindustry.gen.*;
 import mindustry.world.blocks.*;
 import mindustry.world.blocks.ConstructBlock.*;
 
 import static mindustry.Vars.*;
 
 public class Build{
+    private static final IntSet tmp = new IntSet();
 
     @Remote(called = Loc.server)
     public static void beginBreak(Team team, int x, int y){
@@ -36,7 +39,8 @@ public class Build{
 
         tile.setBlock(sub, team, rotation);
         tile.<ConstructBuild>bc().setDeconstruct(previous);
-        tile.build.health(tile.build.maxHealth() * prevPercent);
+        tile.build.health = tile.build.maxHealth * prevPercent;
+
 
         Core.app.post(() -> Events.fire(new BlockBuildBeginEvent(tile, team, true)));
     }
@@ -55,11 +59,23 @@ public class Build{
 
         Block previous = tile.block();
         Block sub = ConstructBlock.get(result.size);
+        Seq<Building> prevBuild = new Seq<>(9);
 
         result.beforePlaceBegan(tile, previous);
+        tmp.clear();
+
+        tile.getLinkedTilesAs(result, t -> {
+            if(t.build != null && t.build.team == team && tmp.add(t.build.id)){
+                prevBuild.add(t.build);
+            }
+        });
 
         tile.setBlock(sub, team, rotation);
-        tile.<ConstructBuild>bc().setConstruct(previous.size == sub.size ? previous : Blocks.air, result);
+
+        ConstructBuild build = tile.bc();
+
+        build.setConstruct(previous.size == sub.size ? previous : Blocks.air, result);
+        build.prevBuild = prevBuild;
 
         result.placeBegan(tile, previous);
 
@@ -110,7 +126,9 @@ public class Build{
             for(int dy = 0; dy < type.size; dy++){
                 int wx = dx + offsetx + tile.x, wy = dy + offsety + tile.y;
 
+
                 Tile check = world.tile(wx, wy);
+
                 if(
                 check == null || //nothing there
                 (check.floor().isDeep() && !type.floating && !type.requiresWater && !type.placeableLiquid) || //deep water
diff --git a/core/src/mindustry/world/Tile.java b/core/src/mindustry/world/Tile.java
index a8893088f8..978d91fe58 100644
--- a/core/src/mindustry/world/Tile.java
+++ b/core/src/mindustry/world/Tile.java
@@ -389,19 +389,27 @@ public class Tile implements Position, QuadTreeObject, Displayable{
      */
     public Seq<Tile> getLinkedTilesAs(Block block, Seq<Tile> tmpArray){
         tmpArray.clear();
+        getLinkedTilesAs(block, tmpArray::add);
+        return tmpArray;
+    }
+
+    /**
+     * Returns the list of all tiles linked to this multiblock if it were this block.
+     * The result contains all linked tiles, including this tile itself.
+     */
+    public void getLinkedTilesAs(Block block, Cons<Tile> tmpArray){
         if(block.isMultiblock()){
             int offsetx = -(block.size - 1) / 2;
             int offsety = -(block.size - 1) / 2;
             for(int dx = 0; dx < block.size; dx++){
                 for(int dy = 0; dy < block.size; dy++){
                     Tile other = world.tile(x + dx + offsetx, y + dy + offsety);
-                    if(other != null) tmpArray.add(other);
+                    if(other != null) tmpArray.get(other);
                 }
             }
         }else{
-            tmpArray.add(this);
+            tmpArray.get(this);
         }
-        return tmpArray;
     }
 
     public Rect getHitbox(Rect rect){
diff --git a/core/src/mindustry/world/blocks/ConstructBlock.java b/core/src/mindustry/world/blocks/ConstructBlock.java
index d6bb877be8..3cd0b5ec0f 100644
--- a/core/src/mindustry/world/blocks/ConstructBlock.java
+++ b/core/src/mindustry/world/blocks/ConstructBlock.java
@@ -5,6 +5,7 @@ import arc.Graphics.*;
 import arc.Graphics.Cursor.*;
 import arc.graphics.g2d.*;
 import arc.math.*;
+import arc.struct.*;
 import arc.util.ArcAnnotate.*;
 import arc.util.*;
 import arc.util.io.*;
@@ -62,6 +63,7 @@ public class ConstructBlock extends Block{
         if(tile == null) return;
 
         float healthf = tile.build == null ? 1f : tile.build.healthf();
+        Seq<Building> prev = tile.build instanceof ConstructBuild ? ((ConstructBuild)tile.build).prevBuild : null;
 
         tile.setBlock(block, team, rotation);
 
@@ -71,6 +73,10 @@ public class ConstructBlock extends Block{
             if(config != null){
                 tile.build.configured(builder, config);
             }
+
+            if(prev != null && prev.size > 0){
+                tile.build.overwrote(prev);
+            }
         }
 
         //last builder was this local client player, call placed()
@@ -126,6 +132,7 @@ public class ConstructBlock extends Block{
          * If there is no recipe for this block, as is the case with rocks, 'previous' is used.
          */
         public @Nullable Block cblock;
+        public @Nullable Seq<Building> prevBuild;
 
         public float progress = 0;
         public float buildCost;
diff --git a/core/src/mindustry/world/blocks/distribution/Conveyor.java b/core/src/mindustry/world/blocks/distribution/Conveyor.java
index 351ab3b773..f6f347aba3 100644
--- a/core/src/mindustry/world/blocks/distribution/Conveyor.java
+++ b/core/src/mindustry/world/blocks/distribution/Conveyor.java
@@ -146,6 +146,20 @@ public class Conveyor extends Block implements Autotiler{
             }
         }
 
+        @Override
+        public void overwrote(Seq<Building> builds){
+            if(builds.first() instanceof ConveyorBuild build){
+                ids = build.ids.clone();
+                xs = build.xs.clone();
+                ys = build.ys.clone();
+                len = build.len;
+                clogHeat = build.clogHeat;
+                lastInserted = build.lastInserted;
+                mid = build.mid;
+                minitem = build.minitem;
+            }
+        }
+
         @Override
         public boolean shouldIdleSound(){
             return clogHeat <= 0.5f ;
@@ -161,11 +175,9 @@ public class Conveyor extends Block implements Autotiler{
             blendscly = bits[2];
             blending = bits[4];
 
-            if(front() != null && front() != null){
-                next = front();
-                nextc = next instanceof ConveyorBuild && next.team == team ? (ConveyorBuild)next : null;
-                aligned = nextc != null && rotation == next.rotation;
-            }
+            next = front();
+            nextc = next instanceof ConveyorBuild && next.team == team ? (ConveyorBuild)next : null;
+            aligned = nextc != null && rotation == next.rotation;
         }
 
         @Override
@@ -220,7 +232,7 @@ public class Conveyor extends Block implements Autotiler{
                 if(ys[i] > 0.5 && i > 0) mid = i - 1;
                 xs[i] = Mathf.approachDelta(xs[i], 0, speed*2);
 
-                if(ys[i] >= 1f && moveForward(ids[i])){
+                if(ys[i] >= 1f && pass(ids[i])){
                     //align X position if passing forwards
                     if(aligned){
                         nextc.xs[nextc.lastInserted] = xs[i];
@@ -242,6 +254,14 @@ public class Conveyor extends Block implements Autotiler{
             noSleep();
         }
 
+        public boolean pass(Item item) {
+            if(next != null && next.team == team && next.acceptItem(this, item)){
+                next.handleItem(this, item);
+                return true;
+            }
+            return false;
+        }
+
         @Override
         public int removeStack(Item item, int amount){
             noSleep();
@@ -346,6 +366,9 @@ public class Conveyor extends Block implements Autotiler{
                     ys[i] = y;
                 }
             }
+
+            //this updates some state
+            updateTile();
         }
 
 
diff --git a/core/src/mindustry/world/blocks/distribution/StackConveyor.java b/core/src/mindustry/world/blocks/distribution/StackConveyor.java
index 009cc8fbfe..ce77b978df 100644
--- a/core/src/mindustry/world/blocks/distribution/StackConveyor.java
+++ b/core/src/mindustry/world/blocks/distribution/StackConveyor.java
@@ -2,6 +2,7 @@ package mindustry.world.blocks.distribution;
 
 import arc.graphics.g2d.*;
 import arc.math.*;
+import arc.struct.*;
 import arc.util.*;
 import arc.util.io.*;
 import mindustry.annotations.Annotations.*;
@@ -14,6 +15,7 @@ import mindustry.type.*;
 import mindustry.ui.*;
 import mindustry.world.*;
 import mindustry.world.blocks.*;
+import mindustry.world.blocks.distribution.Conveyor.*;
 import mindustry.world.meta.*;
 
 import static mindustry.Vars.*;
@@ -220,6 +222,16 @@ public class StackConveyor extends Block implements Autotiler{
             }
         }
 
+        @Override
+        public void overwrote(Seq<Building> builds){
+            if(builds.first() instanceof ConveyorBuild build){
+                Item item = build.items.first();
+                if(item != null){
+                    handleStack(item, build.items.get(itemCapacity), null);
+                }
+            }
+        }
+
         @Override
         public boolean shouldIdleSound(){
             return false; // has no moving parts;
diff --git a/core/src/mindustry/world/blocks/power/Battery.java b/core/src/mindustry/world/blocks/power/Battery.java
index d556f584f5..fb70751c18 100644
--- a/core/src/mindustry/world/blocks/power/Battery.java
+++ b/core/src/mindustry/world/blocks/power/Battery.java
@@ -2,6 +2,7 @@ package mindustry.world.blocks.power;
 
 import arc.graphics.*;
 import arc.graphics.g2d.*;
+import arc.math.*;
 import arc.struct.*;
 import mindustry.annotations.Annotations.*;
 import mindustry.gen.*;
@@ -31,5 +32,15 @@ public class Battery extends PowerDistributor{
 
             Draw.rect(topRegion, x, y);
         }
+
+        @Override
+        public void overwrote(Seq<Building> previous){
+            for(Building other : previous){
+                if(other.power != null && other.block.consumes.hasPower() && other.block.consumes.getPower().buffered){
+                    float amount = other.block.consumes.getPower().capacity * other.power.status;
+                    power.status = Mathf.clamp(power.status + amount / block.consumes.getPower().capacity);
+                }
+            }
+        }
     }
 }
diff --git a/core/src/mindustry/world/blocks/storage/StorageBlock.java b/core/src/mindustry/world/blocks/storage/StorageBlock.java
index 0aca99a0b6..29059a25c7 100644
--- a/core/src/mindustry/world/blocks/storage/StorageBlock.java
+++ b/core/src/mindustry/world/blocks/storage/StorageBlock.java
@@ -1,5 +1,6 @@
 package mindustry.world.blocks.storage;
 
+import arc.struct.*;
 import arc.util.ArcAnnotate.*;
 import mindustry.gen.*;
 import mindustry.type.*;
@@ -40,6 +41,18 @@ public abstract class StorageBlock extends Block{
             }
         }
 
+        @Override
+        public void overwrote(Seq<Building> previous){
+            for(Building other : previous){
+                if(other.items != null){
+                    items.addAll(other.items);
+                }
+            }
+
+            //ensure item counts are not too high
+            items.each((i, a) -> items.set(i, Math.min(a, itemCapacity)));
+        }
+
         @Override
         public boolean canPickup(){
             return linkedCore == null;
diff --git a/core/src/mindustry/world/meta/BlockGroup.java b/core/src/mindustry/world/meta/BlockGroup.java
index 24e8166990..2b3434ccfb 100644
--- a/core/src/mindustry/world/meta/BlockGroup.java
+++ b/core/src/mindustry/world/meta/BlockGroup.java
@@ -1,5 +1,5 @@
 package mindustry.world.meta;
 
 public enum BlockGroup{
-    none, walls, turrets, transportation, power, liquids, drills
+    none, walls, turrets, transportation, power, liquids, drills, storage
 }
diff --git a/core/src/mindustry/world/modules/ItemModule.java b/core/src/mindustry/world/modules/ItemModule.java
index 7b3e4033ea..a293942592 100644
--- a/core/src/mindustry/world/modules/ItemModule.java
+++ b/core/src/mindustry/world/modules/ItemModule.java
@@ -180,6 +180,7 @@ public class ItemModule extends BlockModule{
         return total > 0;
     }
 
+    @Nullable
     public Item first(){
         for(int i = 0; i < items.length; i++){
             if(items[i] > 0){
@@ -189,6 +190,7 @@ public class ItemModule extends BlockModule{
         return null;
     }
 
+    @Nullable
     public Item take(){
         for(int i = 0; i < items.length; i++){
             int index = (i + takeRotation);
@@ -204,6 +206,7 @@ public class ItemModule extends BlockModule{
     }
 
     /** Begins a speculative take operation. This returns the item that would be returned by #take(), but does not change state. */
+    @Nullable
     public Item beginTake(){
         for(int i = 0; i < items.length; i++){
             int index = (i + takeRotation);