Check under the hood for the sticker that tells you about the cars compliance to the manufactered year emmisions control. You will find out what sparkplug the Chevy Dealer put in. Use only this plug and nothing else. My friend whom worked for Chevrolet had untold number of cars that were brought in after the owners did their own tune-ups. The customers reported that the car was running weird, rough, ect at idle and did not have the acceration that it should. 9 times out of 10 the mechanics would pull a spark plug wire and see what plug was installed. Those 9 times they would reinstall the plugs that origonaly came in the car (new one of course) and problems were solved. The otherbrand plugs would fit but were the worng resistance for the ignition system the car was set up with. This is were the problems would come from.
my 12v engine needs 4 plugs, as it is a six cylinder, 2 valves per cylinder.
my 16v engine needs 8 plugs, as it is an eight cylinder, 2 valves per cylinder.
my wife's car with a 16v engine requires 4 plugs, as it is a 4 cylinder.