Bob,

We're not sure on a 3-blade prop. It all depends upon the type of flying. We've seen Pattern Flyers using 16x14 two-blade props, but any propeller that will allow the engine to run in the mid-8,000's and fly your plane is OK.

Usually, a 3-blade prop should be used only if you have ground clearance problems. They aren't as efficient in the air as 2-bladers. A lot of times, the rule of thumb to go from a 2-blader to a 3-blader is to keep the same pitch, but go down an inch or two in diameter. It's not exact because blade profile and airfoil have a great influence on the RPM a prop turns.

As far as reverse-rotation is concerned, it's not possible with that engine. You'd need a special reverse-rotation crankshaft, and such is not made by O.S.