A t5 will work with a little modifications. There are several muncie, saginaw, and warner transmissions that will bolt right up. use the search feature, or ask more specific questions. the best transmission for your truck will depend on budget, and how you plan to drive/use your truck.
If your truck has a torque tube, you will likely have to swap out the rear end for an open drive rear.
If you have a 1 ton, or a heavier chassis, you may want a heavier transmission like an A833, which was used in gm trucks with the designation my6. Over drive will give your truck new life assuming the breaks are also in proper working order.
Here is a partial list of transmissions that will bolt up.
Warner T10 4 speed
muncie m21/m22 4 speed
muncie sm318 3speed
muncie sm420 4 speed
muncie sm465 with a little modification 4 speed
Warner t5 5 speed
Kieseler/tremec tko 5 speed heavier duty than t5
A833/MY6 4 speed Overdrive
Clark heavy duty 5 speed
etc
