Thanks Martin!
Your concerns are noted, but I can't think of any substitute for a ball bearing that will support a 1040G (2lb 4.8oz) steel ball! A string or wire tether is not easy to work with, and makes it impossible to align the balls.
I believe the force of impact resonating throughout the entire frame will be better controlled by a solid pendulum supported by precision pre-lubricated steel bearings. Also, the ability for the big balls to spin reduces the wear by offering a full 360 deg. of possible surface area for contact!
If you have a valid alternative, I will consider it!
Eric