Don't use IHasModel. This is your problem. For one your planks block doesn't use it. So no models are applied. Second all Items have a model. So you can just do something like
for (Item item : ITEMS) {
ModelLoader.setCustomModelLocation(item, 0, new ModelResourceLocation(item.getRegistryName(), "inventory"));
}
And in your case since you have meta items don't add them to the list and instead do them directly like.
for (Enum enum : EnumType.values()) {
ModelLoader.setCustomModelLocation(Item.getItemFromBlock(ModBlocks.SOME_PLANK), enum.getMeta(), new ModelResourceLocation(ModBlocks.SOME_PLANK.getRegistryName().toString() + "_" + enum.getName(), "inventory"));
Something like that.