OK...all things considered, if you followed the suggested prop size and ran the motor sufficiently rich...you wouldn't need to worry about head temps.

Again, these are air cooled engines. Unlike liquid, closed circuit cooled engines....air cooled engine temperatures vary dramatically on the ground, in flight, 1/2 way through the flight, etc.

I highly doubt you'd be able to run your motor for 45 seconds, take the temp, then fly it at the same throttle setting and maintain that temp throughout the duration of the flight.

Is all you need is thermocouple and something to record.