You can get 500 HP out of a 331 or 347 but at what cost to reliability? It's EASY to get that kind of power (and more) out of a 408, or 418........even a 393 with the right heads, cam and intake. Check out these guys and order a free catalog from them. Nice book, with all kinds of stroker kits, parts, long and short blocks, etc. Good reputation too.
www.dssracing.com