This is NOT YOUR issue -- but just saying that these old pigs have a lot of history and can be as wonky as you know what!
I had to make this "body shim" just to get the TCI subframe to bolt up to the car --- because the body had been hit in the driver front. The alignment came out perfect -- but I measure everything to the nth degree and have done this kind of work many times. I call this "cut to cure" hot rodding.
I cut this 1/2" plate and then milled it to the actual dimension (thickness) I needed.... Thank gawd I had the tools and materials to do this kind of work!!