We have a 58-note Aeolian Grand organ with a broken drive belt.
Someone installed a solid round rubber-like belt at one time, but
it's deteriorated to the point we can't piece it together.

My best guess is that, since the pulleys are nickel-plated steel,
the original belt was an extension spring.  I'm looking for someone
who can either confirm or deny my assumption and, whether I'm
correct or not, tell me what do I need to replace this belt with
(size, diameter, length, wire size etc, leather, silicone, etc.)
_and,_ even more importantly, where can I purchase the replacement
part?

My guess is also based on the fact that the other pulley has an
extension spring on it and I've seen similar configurations in
various organettes.

Many thanks in advance for any help or advice.

Luke Schaedle
Benton, Maine