OK that makes sense. Thanks for explaining. My plan to shoot 46mm on my P67II is actually kind of on hold. I need to have a 46mm film mask put behind the shutter curtains. It's not available from anywhere. So it is on hold for now. I do have done some 120 spools modified to accept 46mm film yet fit in my P67II like regular 120/220 rolls.
I have some 35mm 100ft Velvia 50 rolls too. I plan to shoot them on my P67ii with my 55mm lens as well. Believe it or not, 35mm cartridges will fit in my P67ii perfectly. I only need a panoramic adapter kit made specifically for Pentax 67 available on eBay to begin to shoot. I guess I need to have paper leader and tail taped to the film. The 35mm cartridge will not have much room for the film and the paper lead and tail together. This is why I hesitated in getting started. How do you do it on a RB? I probably should modify 120 spools to accept 35mm films. Then spool on the 35mm film with paper lead an tail just like 220 films. The only thing I will still need is the 35mm film masks for the film and the viewfinder.