I saw one this weekend at the Lambretta Jamboree in Colorado Springs. In talking to the owner he said it was very straight forward with just a cut in the U bend, rotate and fill in the gap in the pipe.
Post over on the LCUSA lambretta.org and you'll get a response from the owner on how exactly it was done. Might be helpful when you find someone on your side when you do it.
Bike sounded great and was very fast.
