[spudder]

Here are my thoughts on your situation. I would try to locate a later rearend from a '70-'72 Chevy 3/4 ton truck. Most have a coil spring suspension like your truck. More than likely, the rearend will have 4.11 gears. I had one years ago with 3.54 gears.
Using this rearend, will be a direct bolt-in with the exception of the panhard bar. As stated earlier, the later rearends had a boss cast into the upper right corner of the center section for the panhard bar. In your case I would buy an aftermarket panhard that has it's right side mount on the right side trailing arm perch.
Another consideration, the drive shaft might not be the correct length.
I don't think you would like 4.11 gears using your stock transmission. Too many RPMs at highway speeds. An overdrive trans is the cure but pricey. No way would I use a T5 transmission in a 3/4 ton, they are pretty weak and can't stand a lot of torque. An NV 4500 out of later trucks would be a good choice for a manual but they are pricey and very much in demand.
It depends on what you plan to use your truck for. Just cruising is one thing, but if you plan to use it as a truck, put it together with the heavier components.