8.25 "a"

There weren't many A-body models then - Dart, Valiant, Barracuda. A B-body (Belvedere, Coronet, Satellite?) would be several inches too wide, depending on your wheels. I don't recall if B-bodies were even the same 4" D bolt circle (SBP).

Are you sure 8.25"? I know there was a Mopar 8.25" rear, but I recall an 8.75" option for A-bodies. That alone is rare and add in Sure-Grip (limited slip) and you are looking for a rare beast.

If you give up, many posts on adapting a common Ford 8.8" rear (Explorer) for A-body. Apparently, you only have to shorten one side of the housing and can use a stock axle there.