You're correct that those are being simplified for convenience. Yes, the back will simply unscrew. I don't know about the pre-anny models, but on my 1946 Anniversary, I was able to install a 3x4 Graflok with no problem, which simplifies the use of a roll-film holder, if you can find one. For yours, 3x4 double sided holders can be found (you want the ones without the slot) and film is available from Freestyle (or you can cut down 4x5). I don't see why you couldn't remove the back, attach a piece of thin plywood or aluminum sheet with a 2x3 opening, and then attach a 2x3 graflok back.