If you are buying for performance, and on a budget I would look very hard at a small block 408W (A lot of bang for the buck). Call Adam at Precision Engines (family owned business). They build a excellent engine and their customer service is second to none.
http://www.precisionraceengines.com
Whom ever you choose as an engine builder, make sure that when you have a question, or problem you can pick up the phone on any given day, and speak to the man in charge.