Duffy's designation of "Classic" seems to apply to boats made before 2008, when the propulsion system was redesigned and the cabin was reconfigured.
Prior to 2008, Duffy boats had an electric motor with a belt and pulley system driving a straight propeller shaft. The operator's station is along the centerline of the boat directly above the motor and shaft. A rudder is behind the propeller to provide directional control.
From 2008 on, Duffy changed to a propulsion system of their own design called The Duffy Power Rudder™. The Power Rudder is similar to an outboard motor with power being transmitted vertically to a propeller and rudder assembly. This change improved steering and allowed the operator's station to be moved to the Starboard side.