Uppers are the same no matter which 75 lower you have. Ie the 75b (safety) upper is the Same as PCR which is decocker.
Type A 75 slides will not fit on a B frame, due to the parts related to the FPB. The FPB lever has no place to fit into. I've never actually tried it, because it looked like either: a) it wouldn't go on at all; or b) the lever would shear off. I am pretty sure this is not what you had in mind, but if we are covering all bases, someone should probably mention it.
