I have a Ultra Stick that I have put a RYOBI in it. I relocated the firewall back about three (3) inches from original, and used a flat piece of aluminum for the motor mount. The carb protudes through the new firewall. This set-up did not require any additional weight on the tail to balance the plane. I have C & H electronic ignition, and a bigger carb (26 venturi). A plastic dish from Wal-Mart made a very nice cowl to top it off. I have ported the engine only slightly, and currently swing a 18X8 wood prop and produces 7300 t0 7500 RPM. This is an awsome flyer, with almost unlimited verticle. I am currently working on an additional engine that will be ported a little more, and will have a larger intake. Elevation here is 3700 feet. Rumor has it that you don't want to run a ROYBI over 7500 RPM. I will be testing that rumor with that set-up.