I am curious about this as well. I have a 1962 C10, shortbed stepside with the SM-420 4 speed. I have found the switch mount bracket that goes on the transmission, but have not gone any farther with that part of my project.
I had back up lights on my 1963, but they did not come stock on my 1962. The 1963 had the powerglide and the switch was on the steering column near the floor board. It was part of the neutral safety interlock switch assembly.
I guess I should take another look at the bracket I have. See how it has the switch mounted. I haven't looked at it in a few years since it was a low priority on my To-Do list.
