I finally did my measurements with the modified setup with engine running full lean and tuned at best rpm. Idle needle 1 3/4 turns open, High needle 1 turn open. Muffler with stinger outlet reduced to 6 !! mm to meet noise restrictions.

With the restricted muffler, I expected the temperatures to rise way above 150 degrees C, but this was not the case. Both cylinder head and back of cylinder cooling ribs were at a stable 145 degrees with engine at prolonged full bore and plane kept stationary.
Reducing throttle to 1/2, it took less than two seconds for the engine to drop in temperature to below 110 degrees.
No measurements of the front ribbing was made out of respect for the spinning 20x8 prop.