I think 65, but the use of a road draft tube was also based on DSO.
Jim
One data point on road draft tubes.....my 09K SJ hipo Fastback came with a C50F-L carb and non-drilled out carb spacer. Both were for a road draft car, and owner claimed they were both original to the car. It didn't come with the fabled hipo road draft tube though.
Also, car is DSO 61 (Dallas) and engine build stamp is Oct 18, 1964.
Hope that helps.
Rich