When I installed a Tanaka three-piece expansion pipe on my center-mounted 47R engine, the pipe came awfully close to the front tire. Having a spare 29" ROCKSHOX fork, I installed it on my 26" bike. This gave me almost two inches more clearance between front tire and expansion pipe. After cutting the stem and installing the star nut, the 29er fork slipped into place.
The four-liter HT fuel tank had to be relocated, since the Tanaka pipe crosses over the top tube. A new rear rack was installed, and the HT tank will mount on that.
The mounting bracket for the expansion pipe needs rewelding, so it can bolt onto the Scooter guy motor mount.
The goped guys with this engine and pipe said it's loud. I started it up and didn't think it was noisy. Anyways, a stock muffler can slip onto the three-piece pipe,quieting it down even more. Then a hose needs to route the exhaust past the rear wheel.
This bike should fly with the new pipe.