Use to have t-400 trans in it, but being such low gears with a big block, was 3,500 rpm doing 65mph. Might be alright for small block. On my big block I was roasting 7 and 8 rod bearings quick, plus the gas feeding it.
So I decided to go with the 700R-4. Has the lowest 1st gear of any trans, plus it has overdrive. So now i run about 2600rpm @ 75 mph with the stall locked up in 4th gear, which is a alot better.700r-4 needs to be built to handle high HP, can get expensive.
If you are building 350 might wanna think about stroking it 383ci. 383 are real good nitros motors. If you gonna drive it on the street you got to have a overdrive trans. If not you will be changing bearings all the time cause you will burn them up holding high rpm.
The best thing I did besides using the 700r4, was making it full roller motor.
It is the only way to go if you are going to be racing, but can get expensive also.
A well built auto trans will roast a manual trans in a heartbeat, due to no shift time and no power loss with right stall.
