If you have the eaton rear axle, the pumpkin is removeable and you can replace it with a pumpkin from a 3/4 ton up to 72.
The corp 14 bolt rear should work without too many problems. Measure the distance from springpad to springpad - then see if you can find a 14 bolt with that same dimension, it should bolt right up. You MUST get a dually rear if you want to bolt up the dual rear wheels from your truck. Dually axles are shorter than the single wheel axles. There are a number of different gearsets made for this axle, so you should be able to find what you want. If you really want to increase your top end, find an axle from a diesel rig - these had 3.73, 3.43 gears.
It is also possible that a dana 60 or 70 rear may fit in your truck (other makes have them too, so check under those trucks)- just make sure that the spring pad width is the same.
