For the Endstone Smelter, since there are 2 smelting slots, perhaps allow input for each slot from its respective side, while leaving the top as it is. This way if you are using it for things like iron for duplication/triplication you can put a stack on each side, and it will work. Currently if you put a stack in a hopper feeding in from the top, it fills the left side and then the right side. This makes automation with the Endstone Smelter impossible.