A-904+rear end, HP ratings

Is it an F-body wagon? If so, I think I read something that said that an F-body rear is the same width as or really close to a '68-'70 B-body which means all you need to do is cut the spring perches and move them a .5 inch inward. If it's a V-8 car it should have an 8 1/4 rear.