G-body frame/suspension question
 

Are all the 87 G-Body cars in general, possibly able to handle HP/Torque of a 455 or will they need a lot of reinforcement ? (Cutlass/Monte/Grd Prix/Buick)!!!

Throughout the years on the various G-Body cars of all brands there were a lot o different braces and supports installed. There were some that used bracing behind the seat, in the radiator support area, by the rear shocks etc. Any extra reinforcement is going to help out.

I put a 500 Cadillac in a '87 Cutlass. I drove it pretty hard but I never used slicks. It did have posi. The rear is a 8.5 out of a Grand National. It has a Turbo 400 trans naturally. I haven't broken or bent anything yet. The installer shortened and used the original V6 driveshaft and it hasn't broken either.

A/G body reinforcements
 

In the nineties was heavily into the "metric" malibus, those boxy 78 - 81 coupes. Used to install bars that were apparently only on BOP A/G cars onto those malibus. The bars went from underneath the front crossmember, to the front frame horns on each side. Have heard them called "jounce" bars by some on the now defunct malibu racing site.

There are a lot of factory and aftermarket options. Shotgun Bob of Casual Restoratio s made this very helpful diagram.

https://buickturboregal.com/g-body-regal-frame-braces/