I am running Autolite AR13 plugs with my MSD 6al Box. I know the motor is running rich at low speeds and have never checked plugs after a full throttle run. Having a miss above 2500 rpm and thinking of trying next step hotter plug to help burn off excess fuel.(90% of my driving is in the 2500-3000 range) Trying to figure out next hotter heat range to use. Here's a photo of what my plugs look..
Engine: 427 + .060, 12.5:1, running tunnel with two Holley 650HP series. Don't know the jets installed at this point.