FYI, 10 years ago (or whatever) I bought a brand new military surplus chassis from a supplier for right at $1000. Brand friggen new. It was just normal steel only painted black.
I'd say, unless you get a ridiculous deal (sub $500), go with a new Galvy chassis. Yes, it is expensive, you get what you pay for.
In terms of this chassis, take a ball peen hammer. Just go around the chassis, tapping it. Concentrate on areas near tires. Take a small flashlight (the ones for looking into rifle barrels would bring the win for this) and look in the inside. Basically, these chassis rust from the inside out. So you are looking for weaknesses. This is assuming it is an OEM or original chassis.
Personally I wouldn't buy a used chassis that came on the truck in the 1960s or 1970s. Too much work to go into it just for it to crap out on you 5 years later...or sooner.
