Excuse the poor perspective photoshop edit, but in the future I would love the option to craft/spawn only the insides of a regular furnace. Also the ability to craft a coal-chute to place within a limited distance of the furnace insides. I made a few concepts as to what this could look like:
As for the first concept(the bricks) realistically you would not be able to place the furnaces so close due to the depth of both their insides colliding with each other. UNLESS There was a less deeper version of the furnace-insides?