I have a guy here locally selling a set of freshly rebuilt GT40 heads. My question is how much of an improvement are those over the stock heads on my '92? He is asking $300obo are they worth the money for the power gain? Is it that much over stock ones or am I better off spending the money on some Trick Flow 170's or AFR's? I know heads are a big increase in power but if the GT40 style are a minimal gain I don't think it's worth wasting the money? Anyone with some insight?