On all of them check the engine number. If it has an "H" in the middle it is a high compression (8.8:1) if it has an "L" it is a low compresion (8.3:1).
I had one "L" and it was Lil bit less powerful, could feel the difference.
IMO, for the years mentioned, the 71's had better engines, but the roundies are more attractive.