1962 Dart 8 3/4 rear found

Would the early Dart rears (1962) fit up to the 1970's Mopar A bodies?

Sure, with a lot of work. It will be about 7 inches too long, it has tapered axles and the brake assembly is held on by a nut, and the perches would need moved.

But, it "might" have a suregrip center, so that's a plus.

Essentially, shorten the housing to A body length, install the perches in the proper place, you would need new axles and brake assemblies.