ffkiwi - thanks. I thought I saw one or more of my glowheads having some knurling on top around the stem. After reading your post I looked in my bag of glowheads and sure enough there it was. I have no clue if it works - didn't put any juice to it yet. I have to get some prop bolts before I do anything else.
A few years ago I put together a Black Widow on my test stand. I changed out every cylinder I have until I found the one that gave it the highest RPM with whatever prop/fuel I was using. So somehow I was attaching a prop but I can't find a 5-40 bolt anywhere in my ten gazillion pieces of hardware and none of my .049's have a prop bolt. A couple have that stud and I don't even know if it comes out or not. It's stuck solid in all my engines. Will take a good soak or heat to loosen them up assuming they are supposed to come out.
Thanks for the post. It was very helpful.