It does look like the gear is on back words ....I have 3 of these planes and the best combo for speed and power is a ys 110fz and a apc 13.5x12.5 works great for me ...The os 91fx with a apc 13x8 prop is a good combo.....If you can put a 61 in it you can put a 91 ....They are the same physical size... However the Pitts muffler four the 91 is alot bigger......JW