I have a muffler running on my test stand for several hours. It is a tangential expansion type with nothing inside so nothing will come out. I can stand next to the engine running witout the need of ear plugs.
The only critical issue is dimensions, which sometimes go against intuision.
Feel free to copy it.
 
 
Richard Sohn
N-2071U
 

***** Hi Richard, that is one big starter motor on your single. Do you intend to use it? I have a stock 13b starter for my single but would like to have a smaller unit. The Skytec on my Stinson is even smaller than the Mazda, so maybe we can adapt a smaller unit from something else. BR, Dave McC