Ok. The 3 5/8" measurement between the tabs is what led me to guess a 1330, the 1310 is about 3 1/4" I think. But it was cramped and dark and i was using a measuring tape without any reading glasses, so I could have read it wrong.. I'll have to recheck it.
The rear end doesn't appear to have ever been changed. Nor anything else on the old beast! But who knows after 50 years..
The driveshaft shop said the measurement would tell them which yoke it had so I'd better be sure. He did say that he only needed the width between the tabs and I thought he said it might have a different style if it were a posi vs a standard diff. But I don't remember exactly what he said about that, I might have heard him wrong. I am not sure if this one is a posi or not, but I'm suspecting not.