What cu. stroker would you pick?

For a streetable combo, meaning pump fuel and reasonable manners, I'd go with the 4" crank setups. You can go longer, I havent built one but Dave's (DJV) hase that nice write up on his. In terms of power and head flow, I really think it' a mistake using the RPMs in any form. I have a couple that I am familiar with that run stage 3 Shady Dell RPMs, that were worked beyond that and move 300cfm... But they really are close to maxxed out and they barely make 550-600hp. I would sell what you have and step up to something more racey like the Indy 360-1s and have them ported. A good race head, with a milder solid roller cam, will go a much longer way to making a streetable 600-630hp on pump fuel. You'll also need to lose that 9.5" convertor and get a good 8" race unit.