400 BB build

I say just rebuild the Long Block back to stock specs (advertised 8.5:1 compression) and Blowthrough Single Turbocharge it.....600+ tire frying hp/tq, and better gas mileage (if you could just cruise it) than you'd believe on pump gas.

Otherwise.....stroke it with a 440 crank, buy custom CR pistons a rupity .500ish" cam, and GET A 1000cfm carb and 2" primary headers and crank it up.

NA horsepower and torque numbers are usually half of turbocharged setups....unless drastic modifications such as High CR, Extensive Porting and Polishing, and extensive balancing, are performed....and UN-NECESSARY with forced induction setups unless trying to squeeze out every single hp.