{
	"forge_marker": 1,
	"defaults": {
		"model": "minecraft:cube_all",
		"textures": {
			"all": "minecraft:blocks/diamond_block"
		},
		"transform": "forge:default-block"
	}
	"variants": {
		"normal": [{}],
		"inventory": [{}]
	}
}


somewhere in preinit do:

ModelLoader.setCustomModelResourceLocation(Item.getItemFromBlock(BLOCK), 0, new ModelResourceLocation(<registry name of block>, "inventory"))