GM's 2nd gen F-bodies suffer from torsional twist due to their half frame design and from engine torque as well as from suspension loads.
PTFB's G-braces triangulate the frame to the rest of the chassis, these easy to bolt in braces have proven indispensable in any performance application.
The enspiration for these braces come from a renoun GM engineer, PTFB modernised and improved upon the design to fit 70-81 F-bodies.
Fit with stock A/C (on some early cars may need a valve relocated)
Fit Pontiac engines with tall valve covers.
Fit Small block Chevy.
Fit most LS applications depending on coil pack location and covers.
May NOT fit some Big Block Chevy applications. 
NOTE: solid body bushings are required.