An air valve can be adapted to shift the 2 speed axle itself, but if you are talking about the part that shifts the speedo gears, I don't know of anyone ever having a fix for that. By the time parts were not available, no one seemed to care how fast they were going. Electric two speeds used an electric unit to change speedo gears. It wouldn't be original, but you could probably shift the 2 speed with vacuum and the speedo with electric. I have a 53 with a vacuum. I have never really paid any attention to the speedo.
