I've got a ryobi 31cc jag conversion that I was going to use in a bud nosen citabria. The plane is similar in size, the wingspan is a little longer, than the dynaflite decathlon. Alot will depend on the final weight but this engine should fly the plane scale like. I'd try to keep the airframe as light as possible. I'll probably go with an 16-8 or 18-8 prop with the ryobi. If I was going to spend more money on an engine I'd probably go with the rcs 1.8 or zdz 40B. A zenoah g23 / g26 would also work or even a 3w 24. I chose the ryobi because I had an old string trimmer laying around (BTW ryobi trimmers are junk..I'd only buy another one for the engine) and thought it would make an interesting conversion project. I have yet to get my engine started, I tried starting it by hand and had no luck. I've been told that they will start easily with an electric starter. I thought about converting it to electronic ignition but can't justify the added expense