I put backup lights on my 55 2nd. I bought the kit off of ebay. I believe it is a kit for 55-59 trucks.
It has a collar that goes around the steering column and a bracket that fits on the shift rod (I have the three speed on the column). When the truck is shifted into reverse the bracket mashes down on a plunger on the collar around the steering column and turns on the back up lights. It also came with all necessary for a floor shifter.
When I bought the kit it was missing a lense, bezel, and screws. The screws were barrel screws which were extremely hard to find.
I have pictures but do not know how to post them.
Yesterday I searched the internet for overdrive parts and a classic chevy parts place sold the steering collumn part for somewhere around $12-15. Unfortunately, I don't remember the site. I will check my search history and look for it if anyone is interested.
Best of luck,