The Rimfire sparkplug referred to has a 1/4-32 thread just like a glow plug. So, no rethreading is needed. I think the premise is that the lighter weight of a 2 stroke glow converted to gas with an electronic CDI will result in a more power per unit weight than the weedeater engine. Be careful, because the converted glow will run hotter than on glow and has less cooling fins and mass than the gas engine. So, insure you hae adequate cooling if going this way. Running a gasoline engine on gas/glow will not have cooling problems because it was designed for hotter running gasoline. It will be heavier for the same reason, more cooling fins, and because it has a heavier crankshaft and connecting rod with roller bearings etc. The Walbro gasoline carb will be heavier than the glow fuel carb also. You will need to run heavier percent of oil with the converted glow engine because it does not have roller bearings in the con rod. These are all just general considerations when thiinking glow vs gas vs gas/glow and the conversion permutations involved in each. I think more research and experimentation is needed to see if anyhing but a glow engine will be ok for your designed-for-glow application.

Have you considered electric power? I don't do electric myself, but many do.

Good luck.

Sincerely, Richard