I used that same motor and made the convert to a 454, while doing a rebuild its not that much more money to get the cubes. Heads may be the "unshrouded open chambered" that could put your existing compression at about 8.5 to1. I had the block sonicly meassured and the machine shop made small adjustments to the bore to keep even wall thickness, again not alot more money than a standard rebuild, but with whats left I think I can "a-bore no more".With good bolt ons and in good tune im guessing 400-425 streetable HP. No blower or nos and I keep under 6000 rpm
paul