Unless you gear the 26 drive you'll want something in 40cc's and up for a 22 inch prop. Not what you are looking for though. You could spin a 20 inch with the 26 but over heating the engine becomes a clear factor. perhaps a 35cc engine for a 20" prop, but now the engine is getting heavier. Think some more about using the smaller engine and prop. Perhaps you could cut down a 20 to 19" and have things happy, happy, but only experimenting would prove that.