RE: header length for pattern - max RPM or not
Lots of great information here.
Try the K&B 1L glo-plug. I have been running them for 35 years or so. Typically I get about 60 flights per plug, the element of the plug should never be distorted (or deformed) or you are too lean or too short or both. I usually notice the idle getting a bit ragged when it is time to change a plug, the transition from idle to full speed may also suffer (seem rich). I have run several Bully engines (slightly modified Webras - two plug head) in the 1.20 and 1.45 displacement. The factory low end setting was always too rich, on one occasion it was so bad you could not throttle up unless the glo-plug igniter remained connected.
Good luck!
Will B.