Jon V
I'm about to do something that I see other people do & get irritated at. AND that is to recomend something unsolicited and off topic. Having said that , I can't help but recomend an Irvine 53 over the OS 50SX, especially if you can order from Just Engines easily.
I have had 3 Irvine 53's & love them. ON a pattern plane run it with a tuned pipe at 20 inches( going by memory -I could verify the length if need be) and turning a 12X11 APC prop at 10,000

Eddie