Stiffen and Tie frame 69c1o

[Dans69]

Im running a stout 496 with a BTE turbo 400 and 4.10 gear. I have broken 2 bellhousings. One stock trans case and also a JW Ultrabell. Good solid motor and trans mounts, and the frame is dead straight but stock. Im gonna box the lenght of both frame rails. MY QUESTION IS what is the best method to tie the frame rails from the tail of the trans to the rearend? Truck has really tough drivetrain and a good driveshaft with billet yokes. I just want to keep from braking stuff every time i put sticky tires on it. advice needed and appreciated! THANKS