I dont think the head has anything to do with overheating..It might have more to do with the reading your temp sensor is giving..have tried to completley disassemble the carb to be sure there was no debri caught in the jets??? Air can be drawn into the engine thru the front bearing if the seal is bad, air can leak past the rear engine plate behind the pull-start recoil. In fact, there are two places in that area air could get by. 1) where the starter shaft passes thru the back plate there is an O-ring. 2) around the back plate there is another O-ring that could leak.. Just remember, When you re-assemble these parts, use a thin coating of grease to help the O-ring to slide in without binding or getting caught by an edge..If you search the forum for sealing a nitro engine you will also find that there is a mod that requires a thin coating of silicone gasket sealer on the mating surfaces of the engine parts, to seal air leaks of imperfect part machinig/mating,,Check it out!!
As far as the leaking head goes, check under the shims that should be under the head button. Look for any burrs, debri or even scratches on the mating surfaces. no mater how small the defect is it could be enough to cause air to ge by,,, Believe it!!!
good luck and congratulations on your enduring persistance to tryt another gallon of fuel before you give up..
If all else fails send the engine to me and I will find and fix the leak..I promise.. [8D]
