8.75 rear end

Have the current axles and drums drilled to large bolt pattern. There are some that will comment that it's not safe. I raced a car running 12.0 or better for a few years with a set.

If you don't want to go that way, you'll need to either buy moser/yukon/aftermarket or find some c body or truck axles and have them shortened up and resplined. Local place here charges $100 to shorten/spline