RE: Test stands for break in (not good)
I have been measuring a couple of fins down from the top trying to hit about the top of the chamber against the cylinder wall (not the fins). The in-flight testing I have done has shown this to be about the hottest part. (especially the back side of the cylinder not facing the wind so to speak) I used to use a sensor under the spark plug, but my friend took it back. If you can place a sensor on the cylinder wall where I did you will get an accurate enough number. Some engines can take the heat, others can not. I have one particular garden two stroke that has been running about 380 @ WOT for the last 15 years.
Venom used to make a wrap around sensor that was strapped to the cylinder wall and recorded High, Low, and current temps.
In the picture you can see what I am talking about, the actual sensor is on the back side of the cylinder.