A slant 6 will blow up a 7 1/4 so with a V8 you're on borrowed time unless you're going to just putt around. Finding a stock A-body 8 3/4 is getting tougher all the time. An 8 1/4 is ok for up to 300HP but has many design shortcomings.....C-clip axles and axle bearings that run right on the axle shaft....for instance. If you plan on getting aftermarket axle shafts anyway, you might want to see if you can find a C-body, Van, or pickup 8 3/4 rear. Have the housing narrowed and spring perches welded in the correct spot for your application by the company that supplies the axle shafts. That way there is no arguement if there is a fit problem. You might even have a place in your town that knows how to narrow a housing and you'll save on the shipping costs. Just decide on width, order the axles, and then bring the works down to the axle shop so they can narrow the housing to fit.