HI,
The Ryobi is the most conversion for airplanes. The Homelite is also very popular, but you do have to trim the flange from the case. The amount of power produced is dependent on a few factors, such as carb size, muffler and cylinder configuration. Some engines have curves cast above the transfer ports to ease starting. These reduce power output. The two ring ring engines seem to be best. Most of the parts are interchangable, so you can mix and match for best configuration.

Dave