The Dart block is the way to go for sure - especially if you want to go past 418 cubes (IMHO). But I guess it depends on how much power you're looking for.
It isn't that hard to get into the 500+HP range out of a 418, 408, or even a 393 with todays parts / technology.
Are you familiar with DSS? These guys are near me and i've always like them. They offer some great stroker kits:
www.dssracing.com