Duffy's designation of "Classic" seems to apply to boats made before 2008, when the propulsion system was redesigned.
Prior to 2008, Duffy boats had an electric motor with a belt and pulley system driving a straight propeller shaft. The operator's console is along the centerline of the boat directly above the motor and shaft. A rudder is behind the propeller.
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 console to be moved to the Starboard side.