Thanks,

I have an O.S. 50 and 55 but I think the 55 would be best. It can turn a 12x7 or 12x8 prop. I'm going to mount it horizontally with a pitts muffler. I had a Venus 40 with an O.S. 46 inverted and it was a nightmare to start and keep running till I rotated the motor. 4-strokes are much better inverted than 2 strokes. I also have a Saito 100 I could use but that's over 20oz of motor (and nose weight) vs the 16.5oz with the 55+pitts.
I don't mind trimming the cowl to get better motor performance.
I think I'm going to keep the original I have. There is no wharping in any of the parts and the only difference I can see is the front of the wing and the aileron servos are recessed. Some comments I've read is that the 249R has some down inccidence issues??? No Matter....the one I have looks fine. It's only a $139.00 ARF