I have a 1990 short bed 2wd with a factory 350 and an NV3500. It drives OK, and is "fun", however its not what I would call a "sport truck". I have read loads of reviews that the NV 3500 is not a "strong" box, however I think that relates to the fact that you can break anything if you plant it and dump the clutch.
For more strength I would look at a muncie 4 spd out of a camaro etc., but as said you will need to play with gear ratios, tyre diameters etc. to get a good balance of cruising speed on the highway, without sacrificing pull away from the lights.
Any built trucks going forward however are going to get a Tremec T56 - its a current 6 speed manual, and also a "camaro / pontiac" type box. Advantages include its modern so parts available, not electronic, bolts straight up to any 350 / LS combo, and has a wide ratio range. Should be able to get one from a wreckers reasonably easy, and aftermarket support is extensive.
Do NOT use a Muncie SM465 or ( even worse ) 420. As stated above, these are basically a 3 speed heavy duty TRUCK box, with a crawler/ torque 1st gear. Indestructible, but no use for a snappy gear change in a 2wd sport truck.
Good luck - Post pics ! ...