I have a first gen Mamiya RB67, just the Professional version. I currently have a 127mm lens with it. I'm looking to buy a 65mm lens, and I'm not sure if the different bodies have different lens mounts. Is there a specific lens I need to buy that fits onto the RB67 Professional?
..the mounts aren't significantly different across the various versions of RB 67. At least not as far as the 65mm lens is concerned. Any 65mm RB lens will fit any RB camera.
What Neil said.
All the RB 65mm lenses will be fine. Almost all the RB67 lenses will in fact work fine - the exceptions are late model, special purpose lenses like the 75mm shift lens.
The lenses for the RZ 67 system will not work.
SD Extension tubes will not mount on non-SD body. Most later RB lenses came with mounting collar, with which they fit precisely onto SD body. But those rings are slip-ons, so easily removable to mount that lens on older bodies (Pro and Pro-S)