Cannondale serial #: Serial number code: first two digits are the size, next 6 are date of manufacture, remainder are unit number. For instance: SN#54021787121 indicates a 54 cm frame, built on February 17, 1987, #121.

With that information you can write Cannondale for the definitive answer as to the frame type.

Dave
(yes, I know it's an old post.)