You would be better off to spend your money on a set of 440 source heads. To fix a set of old cast heads properly you're looking at spending $1000.00 any way. Unported you should still get 500 horsepower. I have a friend that has a 493 with with lightly ported 440 source heads and is getting 600 horses out of it. For street use I would also recommend a lunatti voodoo cam. I have used them in my engines and loved em!!!