AFAIK, there's no difference in the pressure plate. Theoretically one COULD make the springs a bit stiffer for 220, and there are cameras without interchangeable backs designed to take either type of film where one moves the pressure plate to make the change. I've also owned cameras that did NOT require any change to the pressure plate(the Bronical S2A and C come to mind). I've been told that kits were available to convert A24 backs to A12 and vice-versa, and I think that they just changed the counter gearing. Furthermore, before Hasselblad released the "A" type backs in 1970, Hasselblad only made one model back. The "pre-A" backs have a "peephole" in the back, and require you to advance the film until you see a 1 in the peephole then start the film counter. I've seen published instructions for using 220 film in these backs that involves putting a rubber plug in the peephole, winding a prescribed number of turns before starting the counter, and then resetting the counter when it gets to 12. I THINK that the start distance from the arrows is the same in both types of film. I've only ever used Kodak(although I have some Fuji in the freezer) and 220 does have two sets of start arrows. The first set are usually hashed or otherwise lightly colored and say "for special cameras" or something to that effect, while the other arrows look just like the ones on 120 film.