64 rear end help

Unless your going to drag race and/or act really stupid on the street my recommendation is go for the A body 8 1/4. Bolts in, aprox 1.5" narrower that your stock 7 1/4, more available and much cheaper than a 8 3/4, big bolt pattern and allows an 8" wide rim + 255 tire without mini tubing (may need offset spring hanger kit). Don't forget the added expenses of shortening a non A 8 3/4 axle: new seals and bearings, labor for cutting and welding housing, new spring pads and welding, aftermarket or buy and chop/respline truck/C body axles, plus the drive shaft will need shortening also. That axle swap goes from an idea of a quick and easy swap to a smoking pile of cash, time and fustration. Freshen up a 8 1/4 with new bearings and seals and it will handle a lot of abuse on the street. But if your going with slicks you'd be better off with 8 3/4. Just don't kid yourself that it is going to be cheap or easy getting big tires under your car.