I would build the 400 block after having it sonic tested first and then use a 4.25 stroke crank with what ever size pistons you need to get under 10.7 to 1 compression with the aluminum heads you use. I would use the Trick Flow 270 heads with a matching intake manifold with a 850 CFM carb or bigger and a cam that has at least 250@.050 duration ground on a 108 LSA installed at or around 104 ILC with as much lift you can get and 2.0 inch headers with a 3.0 inch exhausts system