RCIGN1,

I haven't used an insert that replaces the spark plug yet but I've seen them. The glow plug threads are dead center, doesn't look like enough room for a second plug.

Or, do you mean drill and tap directly into the cylinder head?

I'll be making a clamp on head so I can custom make anything I want to try. Easy when you can see the underside.

Thanks for the tip on cold versus hot plug. I assume then that you energize the cold plug to start and then depend on the hot plug to kick in and advance the timing at full bore?

Sounds very workable. Thanks for the ideas guys.

But geez, five plugs,,, flame out the center hole, geez,,, woulda loved to have seen that.

Forgive me but I've been involved in the really itty bitty engines for a while. I assume you're referring to Reno type racing?