The Express/Hobbit flywheel cam cross over to the GY6 is pretty easy. There's a few ways to do it without hard equipment.
Just went and dug out an old stock PA50ii crank. On the Variator side shaft of the crank, slide the cam on then chase it with the GY6 hub. Tighten it snug to allign it so u can see where to drill. Measure and drill or dremel til they fit together then transfer the new GY6 hub holes back onto the flywheel.
Then the Hobbit cam will be pretty close to center. Spin it to get it good then weld it inside and out. That's about it. Clean all that shit uP!!