The Borg Warner T-10 was great behind a 289 Ford or a 327 Chevy. They were not good behind a big block. Your '63 is a rare transmission to sell to a restorer. Their failures are the reason the A-833 was developed.

The Super T-10 is the one in a '70s Camaro. It was big news when they came out in about 1973, because it had quite a bit higher torque capacity.

Richmond Gear has the rights to the Super T-10 and possibly the plain T-10.

I wouldn't put anything less than a Super T-10 behind a bigblock.

R.