Lots of people have used the VVRC 40cc twin in the Hangar 9 30cc Beaver. I'm one of them. It fits inside the cowl without any trimming needed, except for exhaust stacks. They barely protrude outside the cowl. I'm planning on modifying a set of mufflers two make a 2-into-1 header and have it exit at the scale location. That's a Winter project. Still too much flying to do this Fall! The VVRC 40 is a perfect match for this airframe. Hauls it off the ground quick, makes very scale short-field takeoffs, and sounds great. It's pretty rumbly at mid-range, which gives it a beastly and powerful sound. I run a 19x10 3-blade semi-scale prop on mine, and get about 7000rpm on the ground, and I live and fly at 5,800' MSL. Perfect prop to claw through our less dense air at this altitude, and not too much blade to decrease performance. If I were flying a 3D airplane I would have to use a different prop. For the scale Beaver, though, it is absolutely perfect. See pics 3 posts up.