A OS 160 spinning a 17x10 APC at 8.4k powers a 18.5 pound Platt Zero with confidence. If your spit is 20 pounds of less and you don't want to break the sound barrier it should be fine. I had a Saito 180 with 17x8 at 8.4k on a 17.5 pound Claude and it had "Nice power" that is more than scale.

I believe the G-38 will spin a 18x10 prop and the G-45 can spin a 20x10. You might try a 17x12 if you don't have enough speed. A Moki 2.10 using a 20x10 powers a 26 pound P-47 with authority.

Carl