Your '64 Sport Fury would have come with a 8 3/4" , which is plenty strong. If you want to get rid of that tapered axle setup, just swap in a 1968 - 1970 complete rear end. It is about the same width and is a straight bolt in, if you use your '64 rear emergency cables. I have done this with my '64 Dodge Polara's with no problems. This rear end is easier to service brakes, and change pots. If you want to run larger tires, use the narrower '66 - '67 rear end. Visually, it is identical to original, if you leave hub caps on.
Pick-up rear ends are usually wider than a car piece, and mount under the springs, rather than over them as a car does. I doubt if it would be worth all the effort.