I took my driver's license test in a 1979 burb lo these many years ago, and I worked on it extensively. It was the 1500
model however and had the 350 engine, not the 454. Largely the same truck.
You asked for advice, so at the risk of being blunt, I'll say that you're looking too far back in years and would be better off in the long run getting something newer. The rust problem will spread because the galvanizing in 1979 wasn't as good as 1990s and newer trucks, and it's not cost effective to patch or replace panels.
Nothing wrong with running the Durango heavily loaded if that's what you have. GCWR numbers don't mean that much and with the Hensley and a good brake controller you'll be fine.