I know the '54 (and 1st series '55)had the one-piece curved windshield, unique grill, front fenders and hood(?), as well as the flat rail top on the bed. The '54 GMC seemed to have the same grill and fenders as the older models, but also had the one-piece windshield and bed rails. I put a 270 Jimmy in my '54 chevvy PU and found that while the bellhouse would swap, the front mount missed the frame holes by a good inch or so.
