Regarding the plug gap with the MSD ignition, following is the question I sent to the MSD techs and their reply:
Question:
I have a 468 Chevy in my v-drive boat and your MSD 6M-2 ignition system. The plugs are NGK R UR4 V-POWER set at about .036" gap. Are the plugs and gap OK? If not, what would you suggest?
Answer:
We do not have a preference to spark plug brand, brand of choice. We do offer a starting point to get you started
COMPRESSION SPARK PLUG GAP
up to 10.5:1 0.050"-0.060"
10.5:1-13.0:1 0.040"-0.050"
above 13.0:1 0.035"-0.045"
Open gap in 0.005" increments until best performance is obtained. The only thing we do recommend is to stay away from "hype plugs".
Thanks
MSD Tech