TF 727 question

The issue with the exploding 727s relates mostly to low band apply. My understanding is that with a stock valve body in manual low, both the low band and sprag are engaged. In an effort to improve shifting in racing situations, some aftermarket valve bodies do not apply the low band in first gear and rely only on the sprag, if this fails then things can go boom. In this situation, it is advisable to start the burnout in 2nd gear, then you eliminate the risk of failure. These days a lot of aftermarket valve bodies include the low band apply feature for additional safety, probably still a good idea to start your burnout in 2nd gear.

A 727 that is "built" for 800 HP reliability will no doubt incorporate some good quality parts to reduce the risk of failures.

The important thing is that if you're going to have over 400 hp almost ANY transmission needs to be modified to handle the power. If this is to be a street/strip car I'd use a four speed (or more) auto. A later model GM auto with five or six speeds would be better for a street car, but a plain old three speed should be a bit stronger if more strip than street.