About to help a friend build off his stock 302 93 block. He wants to either build a 306 or 331 for a street use, not daily driven car. Looking to hopefully have close to 400 hp, maybe more if possible. As far as cost in relation to hp gains, which would be better to build. Wanting a reliable, natural aspirated, maybe run nitrous engine. Can you all help me on the pros and cons of this build and what parts it is going to take to make either setup reach the 400 hp range. Is it possible for less money to build this engine from a 306? Please list all parts he is going to have to look into buying to reach this goal. Thanks for any help.