Now for your original question. It appears that the 6 bolt hub is screwed onto the front of of the crankshaft. The plate between the 6 bolt hub and the magnet has holes in it with nothing in the holes. It was probably part of the original back pack blower. The magnet may be on a tapered shaft with a key.

Now for my question. If you get the magnet off what kind of special prop hub are you going to have machined? If you are serious about an electronic ignition then ship it to Ralph to have him work his magic. I assure you that it will be lighter and run like a charm when you get it back. I think there is plenty of room in the back, where the points are, to put one of Ralph's ignitions.