5.9 Magnum flywheel - DIY with bolt-on weight??

Perhaps. But I think not. I believe the combined weight removed will act at the center of the area from which it was removed as if it were removed from one large hole at that point. I could be wrong. We need a physics major.

Edit:

Been a while since I did physics but after posting the above, something twigged. The explanation below demonstrates how vector splitting works. Weight removed from a vector off center from the balancing vector has less effect.

So you are correct. Nice observation.

If the angles of the outside holes are measured one could arrive at the total required weight along the balancing vector. Unfortunately I'm tied up with other things for the time being.

http://reliabilityweb.com/index.php/articles/balancing_weights_radius_changes_and_splitting/