go with the big block... I was going to go with the 514, but the 557 stroker kit isnt much more...
big blocks AREN'T more expensive, the stock 460 2 bolt block will handle 600-650HP.. you can make good HP with a set of factory iron heads.. or you can use the e'brocks.. they arent that much $$ really ..
couple places to check out..
http://fordifiedracing.homestead.com/bigblockfox.html
http://www.network54.com/Forum/85220