diff --git a/api/geyser/src/main/java/org/geysermc/geyser/api/event/lifecycle/GeyserDefineCustomBlocksEvent.java b/api/geyser/src/main/java/org/geysermc/geyser/api/event/lifecycle/GeyserDefineCustomBlocksEvent.java
index bc8db82b8..c821c593a 100644
--- a/api/geyser/src/main/java/org/geysermc/geyser/api/event/lifecycle/GeyserDefineCustomBlocksEvent.java
+++ b/api/geyser/src/main/java/org/geysermc/geyser/api/event/lifecycle/GeyserDefineCustomBlocksEvent.java
@@ -54,4 +54,13 @@ public abstract class GeyserDefineCustomBlocksEvent implements Event {
      * @param customBlockState the custom block state with which to override java state identifier
      */
     public abstract void registerBlockStateOverride(@NonNull String javaIdentifier, @NonNull CustomBlockState customBlockState);
+
+    /**
+     * Registers the given {@link CustomBlockData} as an override for the
+     * given java item identifier
+     *
+     * @param javaIdentifier the java item identifier to override
+     * @param customBlockData the custom block data with which to override java item identifier
+     */
+    public abstract void registerBlockItemOverride(@NonNull String javaIdentifier, @NonNull CustomBlockData customBlockData);
 }
diff --git a/core/src/main/java/org/geysermc/geyser/registry/mappings/MappingsConfigReader.java b/core/src/main/java/org/geysermc/geyser/registry/mappings/MappingsConfigReader.java
index 3eb195517..039412957 100644
--- a/core/src/main/java/org/geysermc/geyser/registry/mappings/MappingsConfigReader.java
+++ b/core/src/main/java/org/geysermc/geyser/registry/mappings/MappingsConfigReader.java
@@ -29,8 +29,8 @@ import com.fasterxml.jackson.databind.JsonNode;
 import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
 import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap;
 import org.geysermc.geyser.GeyserImpl;
-import org.geysermc.geyser.api.block.custom.CustomBlockMapping;
 import org.geysermc.geyser.api.item.custom.CustomItemData;
+import org.geysermc.geyser.registry.mappings.util.CustomBlockMapping;
 import org.geysermc.geyser.registry.mappings.versions.MappingsReader;
 import org.geysermc.geyser.registry.mappings.versions.MappingsReader_v1;
 
diff --git a/api/geyser/src/main/java/org/geysermc/geyser/api/block/custom/CustomBlockMapping.java b/core/src/main/java/org/geysermc/geyser/registry/mappings/util/CustomBlockMapping.java
similarity index 90%
rename from api/geyser/src/main/java/org/geysermc/geyser/api/block/custom/CustomBlockMapping.java
rename to core/src/main/java/org/geysermc/geyser/registry/mappings/util/CustomBlockMapping.java
index ccd5e8ad8..a4a525317 100644
--- a/api/geyser/src/main/java/org/geysermc/geyser/api/block/custom/CustomBlockMapping.java
+++ b/core/src/main/java/org/geysermc/geyser/registry/mappings/util/CustomBlockMapping.java
@@ -23,11 +23,13 @@
  * @link https://github.com/GeyserMC/Geyser
  */
 
-package org.geysermc.geyser.api.block.custom;
+package org.geysermc.geyser.registry.mappings.util;
 
 import java.util.Map;
 
 import org.checkerframework.checker.nullness.qual.NonNull;
+import org.geysermc.geyser.api.block.custom.CustomBlockData;
+import org.geysermc.geyser.api.block.custom.CustomBlockState;
 
 /**
  * This class is used to store a custom block mappings, which contain all of the 
diff --git a/core/src/main/java/org/geysermc/geyser/registry/mappings/versions/MappingsReader.java b/core/src/main/java/org/geysermc/geyser/registry/mappings/versions/MappingsReader.java
index a49e9fcc6..d94f78251 100644
--- a/core/src/main/java/org/geysermc/geyser/registry/mappings/versions/MappingsReader.java
+++ b/core/src/main/java/org/geysermc/geyser/registry/mappings/versions/MappingsReader.java
@@ -27,10 +27,10 @@ package org.geysermc.geyser.registry.mappings.versions;
 
 import com.fasterxml.jackson.databind.JsonNode;
 
-import org.geysermc.geyser.api.block.custom.CustomBlockMapping;
 import org.geysermc.geyser.api.item.custom.CustomItemData;
 import org.geysermc.geyser.api.item.custom.CustomRenderOffsets;
 import org.geysermc.geyser.item.exception.InvalidCustomMappingsFileException;
+import org.geysermc.geyser.registry.mappings.util.CustomBlockMapping;
 
 import java.nio.file.Path;
 import java.util.function.BiConsumer;
diff --git a/core/src/main/java/org/geysermc/geyser/registry/mappings/versions/MappingsReader_v1.java b/core/src/main/java/org/geysermc/geyser/registry/mappings/versions/MappingsReader_v1.java
index 99aa08902..f72ef5986 100644
--- a/core/src/main/java/org/geysermc/geyser/registry/mappings/versions/MappingsReader_v1.java
+++ b/core/src/main/java/org/geysermc/geyser/registry/mappings/versions/MappingsReader_v1.java
@@ -31,7 +31,6 @@ import com.google.common.base.CharMatcher;
 
 import org.geysermc.geyser.GeyserImpl;
 import org.geysermc.geyser.api.block.custom.CustomBlockData;
-import org.geysermc.geyser.api.block.custom.CustomBlockMapping;
 import org.geysermc.geyser.api.block.custom.CustomBlockPermutation;
 import org.geysermc.geyser.api.block.custom.CustomBlockState;
 import org.geysermc.geyser.api.block.custom.component.BoxComponent;
@@ -47,6 +46,7 @@ import org.geysermc.geyser.level.block.GeyserCustomBlockData.CustomBlockDataBuil
 import org.geysermc.geyser.level.physics.BoundingBox;
 import org.geysermc.geyser.registry.BlockRegistries;
 import org.geysermc.geyser.registry.mappings.util.BlockPropertyTypeMaps;
+import org.geysermc.geyser.registry.mappings.util.CustomBlockMapping;
 import org.geysermc.geyser.registry.type.BlockMapping;
 import org.geysermc.geyser.util.BlockUtils;
 
@@ -480,7 +480,7 @@ public class MappingsReader_v1 extends MappingsReader {
         return pairs;
     }
 
-    public float clamp(float value, float min, float max) {
+    private float clamp(float value, float min, float max) {
         return Math.max(min, Math.min(max, value));
     }
 
diff --git a/core/src/main/java/org/geysermc/geyser/registry/populator/CustomBlockRegistryPopulator.java b/core/src/main/java/org/geysermc/geyser/registry/populator/CustomBlockRegistryPopulator.java
index f3a75415c..3ff0ac58e 100644
--- a/core/src/main/java/org/geysermc/geyser/registry/populator/CustomBlockRegistryPopulator.java
+++ b/core/src/main/java/org/geysermc/geyser/registry/populator/CustomBlockRegistryPopulator.java
@@ -72,6 +72,14 @@ public class CustomBlockRegistryPopulator {
                             javaIdentifier + " Old override: " + oldBlockState.name() + " New override: " + customBlockState.name());
                 }
             }
+
+            @Override
+            public void registerBlockItemOverride(@NonNull String javaIdentifier, @NonNull CustomBlockData customBlockData) {
+                if (!customBlocks.contains(customBlockData)) {
+                    throw new IllegalArgumentException("Custom block is unregistered. Name: " + customBlockData.name());
+                }
+                customBlockItemOverrides.put(javaIdentifier, customBlockData);
+            }
         });
     
         for (CustomSkull customSkull : BlockRegistries.CUSTOM_SKULLS.get().values()) {