My very first car was a 40 F*^d and I had a Columbia 2 speed rear for it. Yes, there were vacuum operated and used a switch that was mounted to the shift lever (at least mine was) same a truck would have. It worked OK but was pretty slow to operate. You'll need a vacuum reservoir too. I don't recall the ratio's but the original F*#d rear was 4:44 so the bottom was probably about that and I'll guess the top side was approximately 3:75. They were a pretty common way to get those old flatheads to run over 75MPH but it took a while with only 80HP and that was in the DeLuxe model. I had an Olds V8 in mine so it screamed anyway.
