A decent rebuilt 700r4 with a
hydraulic lockup valve in the valvebody,
.500 boost valve,
corvette servo, and
"beast" Sun shell. will be the best bang for your buck. It will handle more than the hp you plan to pull out of your car. Plus, just add the
tv cable bracket, shorter driveline, and a
crossmember.
If you dont want to go through that much a 200r4 is the same length as a th350 and you can get a factory driveline, and crossmember for the th350 and it will work for the th350.
Personally, i love the 700r4 first gear, and the overdrive is awesome.
This is in my honest opinion, 700r4 all the way or t56.