well, i only own one real rc gas engine, and thats a G62 Zenoah, with the RCIgnition conversion package, which is an electronic advance ignition setup. Its a great engine, and swings a 22x10 at around 6600 rpm. Makes lots of power, and idles like a 4 stroke. The only big difference between the two that i've seen are starting and idling. The electronic ignition engines will hand prop, the conversions won't. Idle speed is also higher on the conversions with the magnetos. But, all mine will sit still on grass, and thats all i care about. The homey idles better than the ryobi, but, i've tweaked the carb on the ryobi severely for more top end, so its not a really fair comparison.
If you were to put an electronic ignition on the weedie or chainsaw conversions, i doubt you'd be able to tell the difference between the two. Most, if not all of the smaller r/c gas engines are also used for different purposes, such as chainsaws, and power equipment. The cylinder, crank and head are the same, usually the crankcase is just made a bit more accomodating for mounting, or at least thats my opinion.