If you assume a 25% loss in the powertrain, it would take 500 hp at the flywheel to make 375 hp at the rear wheels. 500 hp is definitely going to require aftermarket aluminum heads and I don't even think you can buy a decent set of complete heads for $1,000 new unless you're holdin' a pistol on the seller, much less everything else it takes to make 500 hp. Time for a reality check.