War, unleaded heads start in 1972, with induction hardening. The valves themselves didn't change but the seats did. If you are not doing a valve job, and it runs well, leave the heads alone. But if you ARE doing a valve job, then add the hard seats, do an exhaust port match, and your heads will perform much better, and be ready for anything. I'll list part numbers for you tomorrow. Your 66 still has regular rockers without rails, yes ? LSG
And if you replace your heads with new aluminum, I want your old iron heads !
Last edited by LSG; 08-09-2019 at 12:25 AM.