My suggestion, if you plan to add power in the futre, is to find a 12 bolt rear end, then have it set up with gears and posi you want. The set up of the gears is someting for someone who knows what they're doing and has the required tools. If you find a complete 12 bolt unit for a full size car, then you can rebuild it, including the brakes, then swap the whole thing out. At the same time you can replace the control arm bushings. If you plan adding really serious power, you can box the control arms to stiffen and strengthen them. That will improve your handling.

The Biscayne is a realatively heavy car and with a lot of power you will start finding the week points in your drive train. It would be a shame to shell a brand new 10 bolt rear end that you have just invested $$ in. It should not be too difficult to find a 12 bolt that would fit.

Pat