One more thing, putting a standard prop on an engine backwards will not turn it into a pusher prop unless you also reverse the engine's direction of rotation, which is usually not practical unless you fly electrics or reed valve Cox engines. Pusher props have a reverse pitch so the engine can run in the normal rotation and have the prop push.

If you take a nut off a bolt and put it on backwards, you still have to turn it the same direction to tighten it. Likewise, if you install a tractor prop backwards, it still pulls, rather inefficiently though.