Get the OS .37szh easy to tune and has tons of power. It is practically broken in at the factory, so you run it rich for a tank or two and let the horses loose.

Now you current engine. It is hard to imagine that with the starter going in the correct direction the engine would fire and rotae in the opposite. Not questioning your intelligence just seems impossible. An engine can spin in either because there are no gears forcing it in one particular direction. With that said I really don't have an answer for the rotation issue.

Get the OS and be happy.