70-81 2nd gen F body Upper Control Arm Mount Reinforcement Plates click for more pics and product details
A lot of people using the 2nd gens for spirited driving, auto-X, road race track HPDE's, etc. want to stiffen up the platform by installing PTFB G-braces to get the best results from aftermarket suspension components. The G-braces substantially reduce sub frame deflection by triangulating from the sub frame to the upper cowl (I have tested G-Braces in "the Lab"). The lower G-brace mount attaches to the inside of the upper control arm cross shaft on the mounting stud.
These Lab-14 UCA reinforcement plates get welded to the frame mount and are designed to serve a couple purposes. The plates make the UCA mount more rigid by adding thickness. The factory mounts were originally designed for most of the force applied to be from the side of the car by the upper control arm pushing/pulling as it travels through it's range of motion. They were not designed for shear force to be applied in a forward/rearward direction by G-Braces at 90 degrees to the UCA mounting stud. This force is constantly trying to wiggle the UCA cross shaft mounting stud.
The Lab-14 UCA reinforcement plates increase the thickness of the UCA mount to provide a more stable base for the UCA mounting stud while also stiffening up the mount itself. ARP 1/2" studs with a wider splined base are sold separately here and work well when used in conjunction with these plates.
These plates are sold as a pair and the left/right are conformed to fit each side because although the area between the studs is flat where the UCA mounts is flat the rest of the mount welded to the frame is not. Hardware is included to hold the plates in the correct position while welding in place which is explained in the installation instructions. ARP studs (Lab-14 modified) to be used as an upper control arm cross shaft stud upgrade with these plates are sold in pairs here. Stock UCA cross shaft mounting studs can be reused as well as UCA shaft hardware that may be included in coil over conversion kits.