PE made a run of glow 100c engines in the mid 90's. They used 2 glow plugs. Later on most folks converted them back to gas to cut down on the fuel carried. Then you would remove the 14mm to 1/5x43 adapter and install a spark plug The other glow plug you pulled the coil out of and just used it as a plug for the hole.
The top of the head was machined flat and the crankcase was colored red