I wouldn't use the D dart as a recipe to follow, there's more streetable ways to make 275-300 plus hp. Mainly head flow, I would go with 360 or magnum heads, I wouldn't use the factory intake aftermarket will make better power.
Has anyone seen Magnum heads at work on a 273? I've looked but not seen a running example anywhere.... I'm about to do it just because its free and I don't care if grenade it or not....