Hi Bob,
Before trying to remove the magneto, take out the 2 HT pickups (to prevent accidental damage). Remove the cast alloy bridge clamp and the RH stud and adaptor (the one recessed into the side of the mag body), then remove the 2 1/4"BSF bolts securing the mag to the back of the timing chest. You should now be able to pull the mag away from the timing chest - the timing chest has a large enough hole for the timing gear to be left in situ.
Regards,
Eddie.