I've put a Tomos bi-turbo on my carrier but it's a weird General Moped variation that goes to the right side of the bike. A puch header diameter is 22 mm while a sachs header diameter is 26 mm so it's different. You might as well buy a sachs header and then get a two piece bi-turbo. The problem with that is that you are doing all of this work very little performance increase. I'd suggest e.mailing Chad Burke he's selling Gianelli pipes for the Sachs and they are alright.
That's my suggestion.