Can I rebuild an Iron duke in a 80' monza coupe? Is it worth trying to salvage? Will it be less work+money to swap it and put a 305v8 out of my Caprice? Tell me about the Iron Duke that came in these vehicles

I'm reluctant to answer your question here because its not 3rdgen related.
But since I've responded, I'll say that in order to swap a 305 you're looking at around $400 for an oilpan, frame plates and motor mounts just for starters(unless you're handy at fabrication). If you plan to retain accessories like power steering an a/c, then look for a couple hundred more for pulleys and brackets.