[lust4speed]

Pontiac used no seal on the exhaust side and a black rubber seal on the intake - so if you see a seal on the exhaust guide then the guides have been cut for positive seals. In conjunction with the original Pontiac setup an O-ring on the valve stem was used just under the valve stem locks and the metal shield. This complete (archaic) system worked okay at best.

Really unfair to call the positive seals a "Chevy" seal since Viton seals were used on WWII aircraft long before the racing community found out how good they worked. I hate Teflon seals in that they pass more oil down the stem and from my experience they wear rather quickly. Viton is definitely the way to go, and when the guides are cut and Viton seals are installed the O-rings and metal shields need to go away since the Viton seals can be damaged with additional limiting of oil on the stem from the O-rings and shields.