Well, I put those plugs in prior to my big trip 13800 Km in 23 days and did not have any problems.
However when I yanked them out to investigate this multiple misfire problem at high load & RPM # 2 & #3 were fouled..
I spoke to the Tech at NOS and another place and they advise it is not the heat range that is critical but the thickness of the strap and blunt nose of the plug so it does not hang into the chamber.
I wish these guys would also just tell you what plug that might be!!!!!!!!!!!!!!!!!!!!!!!
Kojak