Exactly! The ‘76 calipers went to using the same 2.75” piston that the B/E bodies has started using in ‘70. The E’s and some of the B’s used pin style calipers vs sliding, but they all had the larger piston. And starting in ‘76 everything, including the A’s that formerly used 2.6” piston calipers, went to 2.75”. So A’s, and the B/R/F/M/J cars used 2.75” piston calipers from then on. All of those calipers are not the same, there were still pin style calipers and some of the B body calipers, while sliders, have the brake hose inlet in a spot where it will interfere on an A body. I believe the 73/74 B-body sliders are the ones to avoid for A's.
With Classic who knows! They don’t. You could get almost anything
