I turn down the prop washer part adjacent to the engine, and make a ring with the magnet(s) to slip over the turned down part. With two grub screws, I can then position the ring as required. With a 2-magnet hub at i.e. 120 degrees, all it takes is switch the ring around to alter magnet N/S orientation relative to the engine rotation. A totally different ignition then just needs a new ring. The sensor stays where it is now, or any other convenient place.