Wow! I just stumbled into this thread while searching for Serial # info on my C-40.

I purchased my Marathon in January of 2007. I don't know the size but it fits me very nicely and that's all I cared about. I would have had two Marathons to share with you, but by the time I was done arguing with my bride the nice step-through frame Marathon in Craigs list this past Spring had been sold.

The Serial # on this unit indicates that it was built during 1986. I believe it's mostly original except for the tires, rack, lights, and bottle cage.