I cant help you out on the servos because ive never dealt with airplane ones. But i Can tell you hitec ones are compatible with the stock servo horn. Thats what i use on my hitec 625. And yes you are supposed to check the temperature on the Heat sink. I would think it would be impossible to run your engine below a hundred degrees. You may want to check out the device you used to check it with. If its a laser temp gun make sure you get the reading at the glowplug and not the top fin on the heat sink. The engine should run in the 200-230 range. But since your only on your 4th tank you should be still breaking it in and it might run a little cooler.