If you talk to the guys, and girls, at BTO they will help you plenty.
I installed a BTO 700R4 and through the process they considered everything from my carb, cam, etc., to my tire height. I got the correct speedo gear, torque converter, lock up switch kit etc.
Its been 10K + miles and, as they will claim, driving is a pleasure.
Follow their advice, buy the minor extras they offer (TV cable kit, switch kit, torque converter, chrome TC cover (hehehe), etc.), and I think you will be happy, just say'n
I heard they are a pain, called for myself, and never looked back. Very happy.
BTW: I just re-drilled my TH400 cross member about 3/4 inch back. Gutting the TH400 stuff (including the kick down on the gas pedal) was the biggest challenge. The TV set up was a breeze-again, follow their advice and directions.
PM me with ? if you like