I would just look for a Th200 4R. They are pretty common in a number of B,C and G bodies throughout the 1980's. The best, of course, came in the performance models and are the ones to look for. However, a standard model will also work just fine if you don't need ultimate strength, and don't mind a WOT upshift of only 3,000 RPM's. The better ones had an upshift of 4500-5,000 RPM, plus a number of improvements to the valve body, among other things. You can tell what trans you have with the code on the tin tag located on the tailshaft on the passenger's side of the car. You will also need the TV cable, dipstick and tube, trans crossmember, and trans mount from a overdrive G body to install it in your car/truck. That's how I did mine when I did the V6 to 350 swap years ago and it has worked out ok. However, I am currently trying to find one from a MCSS, Turbo Regal or 442/HO as I have issues with mine, and hate the low upshift point. I wind up shifting it manually (on the column!) when I want to go fast. Oh, and like the other GM OD, newer models are better than older ones for durability. Avoid ones found in Cadillacs as they have very soft shifts, and tend to live a hard life with all that weight. Remember that firmer shifts make a trans last longer (to a point) because the clutches slip less.