Survival has a complete 390 rebuild kit for $700. Not too shabby.

Don't believe that just dropping in any 460 will automatically be cheaper and more powerful. In stock form all the 70s and 80s engines are kind of doggy with all the emission regulations put on them. If you want 400hp or less then rebuild the 390. If you want more than that, then the 460 swap starts to become the better option $$wise the further past 400hp you go.