Carter came out with the D and E series AFB in either late 1962 or maybe mid 1963, the 1964 M.W. cars came with the Carter # 3705 "E" series carbs that had the same size throttle plates front and rear.
I'm not sure if they flowed as well as the later bigger AVS carbs on the 1968 and later 440 motors that had no venturi in the rear to impede air flow