Death is no impediment to starring in a commercial-not when you're John Wayne. Coors Brewing Co. enlisted the "Duke," who died in 1979, for a Coors Light spot that broke on NBC late last week. The 30-second spot from Foote, Cone & Belding, Chicago, uses computer-manipulated footage from the 1966 movie "Cast a Giant Shadow." Joe Pytka directed the still-extant actors in the ad, in which a sergeant presses his troops on who belongs to a six-pack of Coors Light. It turns out to be the general, aka John Wayne.