I'm the guy who is producing the balls for Steve Young. I can offer some help:
1) If you want to cut a slit in the bottom hole to allow the ball to slip past the switch adjuster I would recommend an exacto 'haxsaw' blade to cut out a slot. Using end nips might stress the part and could chip it
2) Use the rivets that come with ball and crimp the open end of the rivet on the metal side of the mount
3) Though I can't sell the balls directly I can offer up the snap on masks I use to spray the white dot and the stripe (If you want to alter some originals). Also the file image for the numbers.
Mike V.