if you look at some pictures of car and airplane engines side by side, i think you will probably see one of the biggest differences. the car motors have HUGE heatsinks because there is no prop blowing cool air over it, they arent traveling nearly as fast most of the time and they are usually mostly enclosed in a body and not sticking right out at the front in the open.

i think most airplane engines can have the head replaced with a buggy head, if the engine you have comes in buggy/airplane models. i don't think i would stick an airplane engine in a buggy, but i don't have either, just marine glow engines