I looked at my 53 with a vacuum shift and my 55 with an electric shift and there is no resemblance between the two. I remember a lot of vacuum shifts were scrapped in favor of electric shift. I don't know how they did it. All we ever had were electric shifts to begin with. There is a good chance they changed the whole rear end because salvage yards were full of trucks with electric 2 speeds. I bought a 53 with a vacuum 2 speed a couple of years ago, but I never drove it out on the highway because of no brakes. I have it in the shop right now putting brakes on it. Once I get that done, I will try it and see if it works. If not, I will decide as to whether I want to try to fix it or if I just want to drive it in high range. It's a GMC with a 270 and I don't haul anything with it.