Yes a flywheel can be cut down. However I don't think it will run true without using a mandrel that has a taper to match the taper in the flywheel. Should be easier to machine a new hub and timing ring. Make a plate to glue the sensor to and use a case bolt to mount it. This way the sensor can be located anywhere and timing is a breeze as the ring rotates 360 degrees and is held in place by a set screw. Check out the Echo 2400 thread and the Lathe For conversions thread. Here is a picture of an Echo 16cc I did showing my work. You will need a plug adapter also to use Adams ignition for the CM-6 plug, CH can sell you a box for about the same money if you want to use the regular plug. Ralph at RC Ignitions can fix you up since you don't have a lathe.