You can use the calculator on this page to help determine the proper sized "collector" and even purchase the components here. Without a mandrel to bend the pipe, it's cut, tack, cut, tack, cut, tack until you get the length and contour you seek.
With a sidecar, I'd rather the exhaust exit the other side. Moves all the heat, gases and noise away from the passenger. But maybe you're not that fond of your passenger
and this is an intentional design choice?