By the late 1970s Chrysler was taking one of its nose-dives into near-bankruptcy and build quality was awful. They were however still using their tried-and-true 1960s-vintage engines and drivetrains. Biggest problem aside from rust would be the crude emissions systems of the time, particularly Chrysler's "Lean Burn" system if so equipped. Lean Burn was particularly awful but I'm not sure if that was used in trucks. (If in an area where inspection is not required that crap can be removed.) Now more than 40 years down the road any initial assembly quality problems should have been long since dealt with and your major concerns will be rust and wear.