Pretty soon everyone is going to have you talked into a Pro-Stock mountain motor.
Your first post says you want 400 at the wheels. Coupe5oh's suggestions will get you there. My 306 makes over 400 at the wheels with a stock crank, stock block, flat tops, Twisted Wedge heads, unported air-gap intake and 650 carb.
The key, as someone else metioned, is the right selection of parts.
Andy