GreenSnake: With your block I would keep the cubes to 408, just to be on the safe side. You can get a reliable 500hp out of a 408 by spending a little money.
There's a place near me called DSS that sells nice stroker kits. A buddy of mine built up his 351 a couple years ago and was very happy with their products and service. I believe their 392 & 408 kits started around 1700.00 bucks (4.0 crank, H-beam rods, custom forged pistons, Speed-Pro Moly rings, Federal Mogul Tri-metal rod and main bearings). He went with a Edelbrock Victor jr. intake and Vic jr. heads and was just under 500hp on the dyno. This year he changed to AFR 205 heads and both his HP and TQ figures went up over 10% right out of the box.
Here is the DSS site in case you're interested:
www.dssracing.com