Since I can’t get the body mounted to the rotisserie until the rusted out rear body mounts are fixed, I tackled that job the other day to find that it will be much easier than original thought. I cut open the rear facing side of the brace near the mount to see that there is a second heavier-duty bracket inside, which means I can pretty much just do a cosmetic restoration on this area and it will be plenty strong enough to do the job. The drivers side bolt was spinning free, so it had to be cut off. The sheet-metal cage around the nut rusted away, letting it spin.
I just welded a new nut to a big washer, then plug welded the washer from the bottom into place, then butt-welded new metal over the areas I cut open and were good to go. I’ll finish the rest of the rust repair in this area after its on the rotisserie, for easier access.