Spicoli;
Maybe we are talking 2 different things! The black pretuned mufflers they sell can be used on many different engines. I'm talking about a tuned pipe and header. Typically you have to cut the header to tune the pipe to the engine. Macs offers a pretuned package that is for specific engines due to the header fitting that engine. Granted an OS will probably fit a magnum but it wont fit a Fox.
You go nowhere with a 10x6 prop! Normally a pipe on glow motors is for speed and you want hi pitch props to take advantage of it. Most speed plane use low diameter, hi pitch props. Sorry if there was some confusion.