I just went to my auto parts store and bought whichever plug was stock in a 97 (right in the middle of the years the Vortecs were offered) Chevy pickup. My engine is pretty much a 330 ho but with a flat tappet cam of slightly increased duration. The plugs are almost perfect. One step colder would also work. The insulators come out white with a black spot where the side electrode covers them. They are clean, but don't appear too hot.