73 frame what body will directly bolt in

[Eyegore]

My son just recently acquired a 1973 k5 unfortunately the box supports were cut out to install two twenty gallon fuel tanks and the body has major rust. So he's thinking of separating the frame and trashing the body and replacing with a better body. We know that a 73-75 will bolt in but what about a 76-77 or 78-80?
Your input will help. Thank you.