Not much. Keep in mind the a bodies were considered compact, b bodies intermediate, and c bodies were full size. Mechanically almost everything was bigger due to the size and weight of those cars.
Off the top of my head I can only come up with a few.
Tie rod adjusters can be swapped for more strength/rigidity over a body size.
8 3/4 Rear brakes could be swapped, backing plate and all.
Master cyl and possibly prop valve.
Cruise control could be added to an a body.
I'm sure others may know of more that could be swapped. If you're looking at buying a c body for parts I don't think it will be worth it unless you need the motor and trans.
thanks for the help guys but i'm not a very good at that type of stuff. i've re&re'd all different kinds of motors, but fabbing isnt my strength plus, i'd like the option of going back to a small-block if I so decide.
one other thing: for the rear brake swap, is it a weld on bracket or does it have 4 studs on a flange? the flange being the common part?