The 12-6 is too much prop. That will cause an engine to overheat everytime.
We have one of these engines on a students plane this year. I did the initial running in on the motor with a Zinger 11-7 prop. I had to dig that out of the truck. He had a 12-6 prop for it. Thats a .60 size prop. LHS probably sold it to him.
I gotta say, after running 3 tanks on the ground and then flying it on the 4th tank, I'm not all that impressed with the performance. I've since put 5 or 6 tanks through that plane while training this student. Still not impressed with the performance. I had the low end a little rich for the first 3 or 4 flights, but have since leaned it for a nice transition and rock solid idle. High end is 400RPM down from peak.
It starts on the first flip--everytime. It idles well. It will sit there and idle a whole tank without skipping a beat. It transitions well. Hit the throttle and it snaps to attention without any burbling or hesitation. Runs great. But it's no powerhouse. Mild sport engine at best.