i HAVE A FRIEND THAT BUILDS STREET ENGINGES. HE TOLD ME THAT AFTER USING MOST OF THE SBC ALUMINUM HEADS AVAILABLE THAT HE DISCOVERED THAT THE ELDEBROCK ALUMINUM HEADS WHEN TORN DOWN CHECK OUT WITH ALL THE CORRECT SPECIFICATIONS EVERY TIME. HE SAYS THAT THE ELDEBROCK HEADS ARE THE ONLY HEADS TO CHECK OUT LIKE THIS. SO YOU HAVE BEEN GIVEN SOME GREAT ADVISE GARYS GEARBOX