"....... unless your running a really built 392, or a very healthy (blown) 354 and has a suspension that really hooks and has very sticky tires I would not be too concerned........."

Of course a "....331" bored out 0.080" which will give us around 345". It's getting 8:1 forged Ross pistons, but the two turbos (TD05H-14B) are set for around 9 lbs of boost. Guestimate is 500 hp max at the flywheel with around 600lbs of torque at 4200 RPM......." could also lead to downstream drivetrain problems too

My guess is it's going to be a toss-up between the transmission and the rearend if your torque figures are accurate. Like you siad there is one way to find out.

A word of advice here for that setup. If something brearks it's going the be the weakest link, and there's a good chance might be spetacular wwhen it does. If it's not already figured in I would add the following pieces.....

The best flywheel you can find.

A scatter shield

Drive shaft safety loop