I would look for a 400 block, have it bored .030 over, and look for some Wiseco, Ross, or JE forged pistons in the 11.5:1 compression ratio. Have around .015 taken off the block, and with a Felpro gasket will leave about .045 from piston to valve. Since you are going radical, I would get a forged crank and H beam rods, a Lunati roller cam setup, Victor intake, and a worked Holley carb. That will give you some giddyup. What vehicle will this be going in?