Yes, I agree that those Holgas are a perfect starting point for tinkering. The plastic is easy to drill, file, glue etc. and the cost when ruining one isn't the end of the world. Thought about putting an (Arsat, Kiev, Pentacon or similar) 80mm lens on a 120GN before I ran into my old Bronica again, making the exercise unnecessary. But I haven't abandoned the idea altogether..