I have just obtained a 1994 transitional 75. It's got the B frame, uses B mags, and the slide is very close to a B. The hammer and beavertail are slightly different from my B, but that is most of the difference that I can see externally.
Looking at the FP block (my terminology, not sure if it's correct) there is a difference in the firing pins. I think that it may be the firing pin block safety, but I would like to be sure. I do not have pictures readily available, so I was curious if anyone had pictures comparing the insides of the slides.
Love my Pre-B, but I am hungry to find a classic Pre-B to add to the collection now.
Marv