Your car is a V6 correct? I don't know much at all about the V6 motors, but I've never heard of swapping in a set of 99 heads making an improvement.
"Posterity! You will never know how much it cost the present Generation to preserve your Freedom! I hope you will make good use of it. If you do not, I shall repent in Heaven, that I ever took half the Pains to preserve it."