You would do well to search on the forum and find somelinks to some of the sites where guys have turbocharged V8s. Seriously, I don't think 550 hp or more is out of order with the right turbo, but you will have to upgrade the injectors (FOR SURE) to get anywhere near that. I don't pretend to be an expert on this, but this will be my next engine build. You can go big single turbo (no too big) to avoid the extra plumbing and costs associated with a dual setup or you can run duals. Get Maximum Boost by Corky Bell and Turbochargers by Hugh McInnes. McInnes also has a fuel injection book that is great as well.
The more you learn about forced induction, especially turbocharging, the more you'll realize that it is totally the way to go as far as HP is concerned.
Davy