I did another pass at the truck looking for issues while I was pulling fenders. Along with the damage that was listed in the first post I uncovered a failing cab floor support and a failing cab mount frame bracket.
I'm not enthused about doing a full replacement floor support. I may grind it back and see if I can get to good metal and just weld in a patch instead of ripping everything apart. The cab bracket will get swapped out with one sourced from a local parts yard so that the new mount bushings will have an easier time.