The O-ring groove was eliminated on the 1996-2000 062 and 906 Vortec valves and a different retainer without a shield was used.
The 906 Vortec heads were equipped with hardened exhaust seat inserts which resulted in a increased valve seat margin compared to the intake seats. The increased exhaust valve margin made the exhaust valve sit lower in the head. It was corrected by making exhaust valves with longer tip lengths. The keeper groove was the same distance from the valve seats.
In order to maintain equal valve stem heights , the O-ring groove, O-ring seals and oil shields were eliminated on the Vortec valve stems and the retainer lock grooves were relocated. The tip lengths were changed from .250" intake and exhaust to .289" on the exhaust valves and .260" on the intake valves. The valve face and seat angles should be ground in order to establish the valve margins at .050" intake and .080" exhaust to allow for the difference in valve tip lengths.