My mopeds are back in Seattle, but I have a couple pictures on the internet.
You can just see the line in the first picture on the backing plate about 1 inch up the right side from the cut off portion.
In the second picture, it's a little more clear. This line corresponds with the dotted line on the side of the flywheel at the point of trigger. so you use a timming tool to get the piston where you want it when the cdi triggers and then mount the flywheel with the dottel line lined up with the little mark on the backing plate.