All of these are good points. If it is complete experimentation that you are looking for, then try it and see what happens. If you are only trying to save a buck or two, it isn't worth it. You can get an inexpensive bushing type 40 sized engine cheap. And if you are looking into the 15 to 25 class engines, even cheaper! It isn't worth the hassle. You'll likely spend more on attaining a drive hub. Maybe someone would trade you that car engine for a plane engine????