Shags, my RCM 40 is nearly identical to your plane in the spec department. The RCM has a 63" span. I have flown it quite a bit with an old Saito .40 and a Graupner 12x5, I've also flown it with a Saito .62 and a Graupner 12x7, with the .62 it will do loops where it is nearly out of sight at the top. I use a Graupner 12x6 or Bolly 12.5x6 on the .56. The reason for the side mount is it will get an LA .46 Diesel conversion next. The beauty of the GP mounts is limitless engine mounting possibilities.