I would install one of the "blanK" type which don't have the nipple hole drilled & tapped yet. Screw it in as far as it will go with a little torque applied to seat it firmly. Then drop the hammer onto the drum and mark around the hammer. Then remove the drum and drill and tap it for the nipple in the center of the hammer nose outline. Use a small drill first for a pilot hole so you know it is exactly right, then drill & tap it with a 1/4-28 tap.