Ryan-
I should stop by and take a look some time! Here's my cross-town opinion in the mean time.
The corners look pretty swiss-cheesy and candidates for cab-corner replacement. It's your call, as the corners won't be important structurally, but probably won't get any stronger with paint. Now is the time to buckle down and do the replacement. It's a lot of time for a small benefit, but it will firm up the body for another 50 yrs.
The crack is a bit different as it looks like spot welds would do it. Again, for structural strength, you might wonder why the crack happended where it did and if there's a way to prevent this stress again. If the crack is a manifestation of rust thinning an entire section, I vote for a patch panel.
Good luck!
