So, moving on to the lower control arm mounts.
The GM engineers really dropped the ball. They must have known about the issues that affected the 1st gens yet they continued to use the poor design another 11 years through the 2nd gen run. The lateral forces affecting the lower control arm were transferred to the edge of the sheet metal frame. That's a lot of force on the thin edge. Compounding that, while one side had the support offered by the shoulder of the bolt that actually fit the hole the other side had the threads of the bolt contacting the edge of the frame. So the forces were transmitted through the tip of the threads to the thin edge of the frame, not good.
So even on a daily driver that got bumped into parking blocks on a regular basis the force ovals the holes in the frame where the LCA attached. The rear most hole in the brackets welded to the frame is usually the worst. I've repaired lots of these.
You can see in the pic below the poor design.
Early 2nd gens used the smaller 1/2" bolt shown below while the late 2nd gens used the 14mm shown next to it. Mid 73-78 used 9/16" and most aftermarket stuff I've dealt with is 9/16".
I put together kits with various modified washers and bolts that get welded to the frame. This spreads the load, reduces frame flex and allows transfer of the forces through the shouldered section of the bolt on both sides of each mounting point to a wider edge than the original frame. The kits are kind of on a case by case basis depending on welder available, which version of sub frame, what aftermarket equipment is being used etc.
Ya I know what you're thinking. You could hunt around for the correct bolts, distorted thread locking nuts, and other hardware and then make patterns, cut, grind, drill, etc. but it's easier and cheaper to just buy a kit from me. Yes, it's cheaper. You can't get everything from one place that I'm aware of and you can't get some of the items in the quantities you want. When you figure the items purchased you don't need, shipping for items you can't find locally, gas to drive around to local places searching, and so on, it ends up costing more than I sell the stuff for. AND, I've already modified things to match certain frames and fit snug on quality hardware. I know this because that's what I went through trying to do my car in the beginning and I'm thinking your time is free, if you put a value on your time it's even more of a deal to just buy a kit.
Here's some of the types of hardware that come in a LCA mount reinforcement kit.
Once the pieces are welded to the frame they look like this.