Looking more closely at the picture in the 1st post, there is a timing tab marked in red, affixed to the stator at about 4:30, and an F mark on the rotor just below 3:00. It appears that the leading edge of the magnet would be aligned with the center of the pole piece at the firing point.
Could a 6 pole rotor be converted to 4 pole? Possibly drill out the rivets, drill new holes, and re-rivet?