It's 12 Manufacturers in a 5x5x5 BP. No extraneous parts. No mods necessary. All belts are Mk5, but you can input with a Mk6 and it will work. If you prefer Mk4 belts, it's not too hard to replace the belts on the inside if you look in from the sides. It's kind of walkable. There is clipping, obviously.

All you have to do is set the recipe 12 times, attach power, attach 4 input belts to the 4 green splitters in the front, and attach an output belt to the red belt in the back.

If I've messed something up, please let me know. Also, please let me know if you want me to pretty this up (or if you want me to link to your prettied up version).