Both the original factory GNX rear seat brace and the one manufactured and / or distributed by Kenne Bell have been gone for years unless you find somebody that bought one years back and never got around to installing it. The ones sold by Kirbans will do just fine and it has never been proven that the original GNX and / or GNX style rear seat brace is any better.
The under the hood braces are pretty worthless for any improvement towards tightening the frame / body but do wonders for removing some unwanted squeaks and / or rattles.
In addition to Installing all of the frame braces and the rear seat brace, installing the the missing GNX body bushings and any other body bushings also contribute to strengthening the frame / body relationship and avoiding the cracks that will eventually appear over the rear of the front windows, even on a bone stock car. Even a bone stock car will eventually display the cracks over the front windows.
I am running the Kirban front triangulation braces in combination with a PT&E stock location intercooler and 1 of the 3 braces do not have enough room to clear.
I once asked Mark Savitske at Saitvske Classic Custom whether his welded front triangulation brace would clear any of the deep SLIC's and never got a response.
I am also running Kirban springs, Bilstein shocks, GNX & missing body bushings (bushing #'s 3 & 4 or #'s 4 & 5), Savitske front upper stage 2 control arms with the tall ball joints, BMR? rear upper double adjustment control arms, & Global West rear lower control arms with the spherical rod ends at one end and the special bushings at the other end, 16" GNX replica / Pontiac rims with Michelin tires front & rear, & replica ATR rear sway bar.
Planning on changing out the ATR replica rear sway bar and replacing it with the "HRParts&Stuff" rear adjustable sway bar, & switching out the stock steering box with a Lee Performance one.
This is on a 30K mile turbo Buick and it is as tight as a drum in the corners.
FWIW, IMHO, & HTH
