Using your definition of awsome I'd say your best junk yard purchase would be a complete running Chevy 350. Easy swap and usually the cheapest Chevy V-8 to work on.
283 and 327 have some cache that increases desirability and prices. Used 400's can be problematic. A 350 for a few hundred with a cheap refresh is likely to your cheapest approach to reliable performance.
If you have a 283 or 327 now you may be able to sell it for enough to finance much of the swap.
