even merlin had reduction gears.
why do real war bird need reduction gear? because prop will reach sound barrier if didn't.

some interesting pix for you.

OS engines attemp at reduction gears

http://www.osengines.com/history/ostimeline09.html

Vario Prop - may be solution to your quest?

http://www.aircraft-world.com/prod_d.../varioprop.htm