Or, you could go to a junk yard and steal one off of many different Ford makes. Take a measuring tape with you though, because that 66 takes a 57" axle measured from spline to spline. Most of the newer Fords had 60-62" axles. Or keep your 8" and have it built with 355 gears and a locker or limited slip. That would be your cheapest route, and that 8" will work just fine without breaking even behind a 500 horsepower motor.