The argument of a 331 vs a 347 has been around for a long time. It all depends on who you ask as to which one is better. If a daily driver, most people will say a 331. If they want more power and it is a racing application, most will say a 347. (There no replacement for displacement). If I was in your shoes, I would go ahead and stroke it now, since you probably have to replace most of the internals anyway. It will not cost anymore for the components. It is not out of reach to get 400 + HP out of a well built 331 at a nominal compression ratio, so you can still use pump gas. I found the best price for my kit at
www.jdsperformance.com I would call, ask for Dave and talk it over with him. Let him know what you are planning and I am sure he can help you.
Ron