let's go back to "anything can happen in 40yrs" and think about the possibility that this might not be an a-body axle or even a mopar piece...
granted, i haven't looked at any other diff cover patterns. and 9 bolts certainly points to 7.25 but have you confirmed that there's a chry co stamp on it somewhere?
also, can you pull a PN off the backing plate? i suppose there's a remote possibility that somebody did an ol switch-a-roo at somepoint because of cost, availability or they were a cheap *** and that's what they had sitting around.
