Tony,
You want to look for a '67-'72 GM (Chev or GMC) 3/4 ton pickup with an automatic. It will have coil springs.
That will have a 4.11 rear gear and it will take you less than two hours to do the swap. I drove my '51 at 55-58 mph all the way to and from Syracuse on this rear end and it is heaven for the original 5.14 stump puller owner.
Here's a link to how I did mine:
3/4 and 1 ton rear end swap option - Get it up to 55 and drive comfortably.
