Need a little guidance from the gurus

The Córdoba is a B body car that came with a 8-1/4 rear. I'm not sure if the 9-1/4 was an option that year being the last year of the B body and no big block option. The rear is a bit wide and would require modifications to fit. It would be way easier to get an A body rear to swing in.

The trans, if it is the stock unit is a 904. It may be a lock up trans.