Just to throw a grenade over the parapet.

What would be wrong with fitting a smaller prop. Say a 9x4 then regulating the rpm with the THROTTLE. LESS FUEL TO ACHIEVE THE SAME RPM SHOULD RESULT IN A LOWER HEAT INPUT FROM THE FUEL BURN.

I was told to do this sort of thing by Mr Super Tigre, Senor Garofoli, himself many many moons ago.