Hi Al, long time.
I was wondering how you made out with the plug inserts. This is an older post and I'm sure you've got a handel on things. Anyway, they shouldn't come out of the cylinders as they are part of the unit. I've installed a lot of them, as a repair, in various car, tractor and small engines where the spark plug threads were stripped out of the heads. I noticed that when the head is drilled and tapped that the insert goes in pretty snug. I also like to use a thread locking compound like Locktight 727, I think, the red kind. If they came out of your engine a little, I would take them all the way out and replace them. When re-installing the plugs you should always replace the gaskets as they crush when installed the first time only and use a torque wrench.
The heat from the plug dissipates through the threads into the head and radiates out through the fins. A loose plug cannot disipate heat they way it should and can rapidly overheat. I remember a friends son's old juncker of a Dodge that had a stripped out plug. I told him where to get the inserts and he installed one by himself. A week later he was calling me about a problem with the new plug. It was burning the tip off. He would replace it and again the tip would burn off. The coldest plug available would still burn off. As it turned out, the insert was only holding in place by a couple of threads because the head was so badly damaged. I installed a short plug and it didn't burn off anymore because of better heat transfer. The Kid wrecked the car a short time after that anyway.
So be safe Al and keep flying.