ORIGINAL: Stick Jammer
It's possible that I missed some posts but I don't remember any tuned pipe installs on a rear exhaust engine.
I think I remember one post where the person used a header from an R/C car tuned pipe to redirect the exhaust. Since these are pushers, all tuned pipes will face forward. I am using a simple rubber deflector, it works but doesn't look very good. Someone else mentioned copper pipe from a harware store. For a YS 60, you may be able to find a Byron pipe (made by Mac's). These were designed for pusher applications. Morris Hobbies may have the Rossi version.
Mark