Joe,
You have to take the allen bolt out and the magnet holder has an internal thread that you can use to get a grip. I use the same norton tool for removing the rocker shafts from the head, it is a sliding hammer and does the job nicely. You could make one yourself if you can find or make a stud with the right thread, unfortunately i am away travelling at the moment or I would see what thread it is, however I'm sure some of the other forum members will know.
Good luck
Dave