I suggest you do not mess with it since the cab over is sagging on the passenger side and shows clue to extensive hidden damage above the area photographed. I would stay away from it since the real work is getting strength back to carry the weight of the cab over. Plus that area to gain that strength is not yet uncovered.
Sometimes it's a whole lot easier to make small payments on a good unit than uncovering a nightmare.
Wait till you look at truck price before you buy a TC though. A good low miles Class C is easier to find.