try ngk but when you intend to use it, get atleast 2 heat ranges colder than what stock is to be. if you dont, you will detonate and cause the ground strap to melt off at min. damage.
the best way to select a heat range is to be too cold at first. make a run and then pull the plugs. get a mag. glass and look closely at the porcilin around the electrode.
if you see ANY
peppering there(little black specks on it) go colder. this is the first sign of detonation.