I've puzzled about these sorts of swaps, too. Just looked over my Pro S manual(p. 56-7. The Pro S manual should be available on the butkus site)and found the weird assortment of "P" and "M" adapters that allowed the RB and Mamiya Press backs to get friendly. Kim should check out the Model K roll film back for the Mamiya Press that switched between 6x4.5/6x6 and 6x9(!?).
Originally Posted by michaelbsc