I agree with Gil. The cracks, rust throughs, and the "repairs". Yikes. Will take some talent to fix. The lower frame rails can be cut out and replaced, and that fuel tank bracket will need to be cut off and rewelded on straight.
I wonder. Maybe some sort of air pressurized CLR spray inside the frame, or etching primer...

Yeah the repair aint the best is it lol, All of what you said did cross my mind so thats defenitly getting addressed. I was maybe thinking of filling the whole frame with some of this http://www.bilthamber.com/deox-gel and then getting a good clean out?

Or is that plain stupid