Hi Gordan, after building the Snow engine with the ignition system from Roy, S/S, I can confirm it is really easy do go this road.
He offers a sketch how to make the disc with the magnet.
There is also a small hall sensor tester available in his shop, a very useful tool to check the timing without any high voltage in the system.
So by a beep and light you can exactly control the function and timing of your engine.