I run a 540 CI BBC in a 3100 lb car with stock 1.76 planetaries.
I would just get a good trans man to build ya one...they are around.just got to look a little bit... Don't know what one costs from TCI but pretty sure you will still need to give them a core.Plus if you have problems what would you rather do? Talk to your tranny guy you met at the track, or ship it back to TCI or whomever and deal with that headache.
JMO but I know a very good tranny guy that drag races