How very cool! And so creative! You're just a marvel! (A marble marvel.)

Is there any groove or anything that holds the marbles in place on the bridge? Or is it only the little chains? Where are the loops of wire that you mention? Are they only at the lowest trough of the chain? Oh wait, I think I see them. So it's the sides of the chain that are tricky and still swing? I was thinking at first that it sounded impossible to ever get the marbles to line up, but the little loops of wire are very merciful of you. :D