OK it's that head.. "The self welding head". So all you did was the elimination kit to the head. How did the old jet valves look? It's possible that might fix the lean burn for that cylinder. I'm convinced it was a vacuum leek causing the hole problem on the spark plug. But time will tell all. Be sure to give updates on this problem. I keep running over the problem in the shower. The glass makes a good white board to finger on.
How about a good picture of that plug for us. You can also look in the wiki on how to read a spark plug for help and pictures.