The 71 and the 72 are not a straight interchange. The crank to wiper lingakge are a little different and if you use a 72 motor on a 71 (or vice versa) it won't bolt up to the crank arm. The 71 is the last year for the red epoxy on the front wire, the 72 is left bare (I think they put a plastic cover after that). The direct cowl boltup is the same, and the wire harness is the same. Two speed switches will not work on a var/3 speed, or vice versa.

Mo Mopar was horrible on the interchange between years in the 70's. I'm sure it had to do with sub contractor suppliers.