it's a waste of money buying iridium plugs. just use v-power copper heads. these engines are not tuned to run 50-100k mile spark plug intervals. especially those of you with high mileage engines. 2 dollars per ngk v-power or $9-10 dollars iridium.
i also heard a rumor from someone saying that if you run laser or iridium plugs on this engine you can burn the top of the piston. I don't know if that's true though...don't fix what aint broke people!