This may not help much but TT has a 1.2 two stroke rear exhaust powerplant. If you can locate a wrap around header, Karl Mueller used to make them for the OS 1.6 two stroke as well as the large ST's. One thing I will say about using a tuned silencer on a large four stroke engine is that while it will not help in scavenging the exhaust pulse, it does sound kind of cool. YS 1.40?