I have a Diabolic, 5 years. The 61 2c will be fine. Use a 4 pitch prop, NO higher. You will need to fly this plane slow. Mine had a OS 91 4C surpass, I just changed it out to a YS 110 with a 17 x 4 APC prop. You should be able to mount the engine on a angle (side but low) so the muffler will sit on the center line of the bottom of the cowl. Go to Esprit Model web site and look at the pictures of the plane. espritmodel.com

also Model Airplane News had a review in May 2003 with a OS 61 inverted and stock muffler out the side. 14 x 4 Zinger prob