You could certainly adapt a car engine to a plane with an extended prop driver to clear the carb because most car engines have a fairly short crankshaft. You'd most likely need a T nut to go inside the prop to engage the threads but that's minor. The only reason car engines get to such high revs is basically because they're running with almost no load (what we'd call a shaft run in planes) and by then they're way past peak HP. It'd run quite well loaded down with a prop to around the 20,000 mark or even less. There are many plane engines that run much faster than this and the main thing is checking the safe revs for a particular size prop. Use a CF prop and you have no worries. Just for interest's sake, an 8" APC prop is supposed to be safe up to about 24,000 revs.