The RB67 70mm back accepts only Type II perforated film by default, but you can modify it to accept any film (perf or non-perf). It is an inexpensive modification, but requires some careful work. The process is not reversible.

You'll need: A small phillips head screwdriver, a Dremel or similar rotary tool with a cut-off wheel, and a ¼ inch orthodontic elastic band.

Step 1: Remove the film carriage from the shell and remove the bottom from the carriage. Looking at the bottom of the carriage, remove the two small screws circled in red below:

Step 2: Remove the metal plate held by the screws and the roller.

Step 3: The now-accessible sprocket wheel must now be cut down with the Dremel cut-off wheel. Holding the wheel steady, carefully cut off each tooth, one at a time. Then slightly turn the wheel and cut off the next, etc. The ideal goal, however, is not to merely cut the teeth away, but to create a very shallow groove in the middle of the wheel, where each tooth was. Don’t cut too deep, and don’t leave any sharp burrs, but try to make a slight channel in lieu of each tooth:

Step 3: String an orthodontic band over the wheel, seating it in the slight groove where the teeth used to be. Make sure the band isn’t twisted: it should be one consistent flat surface around the circumference of the wheel. If it is twisted when you first position it, simply carefully untwist it section by section until it is flat. Make sure that it is resting in the grooves, or at least in the center of the wheel (you don’t want it creeping too close to the either the top or bottom edge of the wheel).

Step 4: Reassemble the roller, retaining plate, and two screws. If the band ever slips off the wheel, you’ll have to take these parts off again and re-position it.

The back will now accept all types of film, including perfed, unperfed, and even 65mm. Congratulations!

Note: RB67 backs that have been modified to shoot 6x6 or 6x9 are also all-perf by default. They are even more reliable, as they disable the Mamiya frame measuring mechanism (which depends on the wheel) and rely on variable winding strokes instead, making them compatible with all types of film.