[gearboxx70]

Any tranny should work. Depends on what kind of work you want to get into. The tranny/t-case will require at least one different cross member from the SM465 you should have in there now. And you may even be able to use your current t-case with the auto tranny.
A TH350 is a simple bolt in deal. If you want the column shift option, you'll need a new column (either a used one from another like-year truck, or aftermarket). Or you could get an aftermarket floor shifter like one from Lokar or B&M.
If you want an overdrive gear, you'll be looking at a 700R4, 4L60, or 4L80. These all came with "married" t-cases, but I'm not sure what t-cases will fit them.
You'll also be looking at different drive lines. The back will have to be shorter, and the front longer since the tranny will be longer.
I haven't done this swap myself, so maybe someone else can come up with info on what they did, or a best option.