The unit illustrated by Tim is similar to this (passenger version) Guide 6004 which was available in a version for trucks. These are still out there as NOS or NORS on eBay if you are looking for original or near set-ups. The 1953 Chevrolet Accessories Manual has all the installation details. Most of the vendors carry reprints of this manual. The part numbers given in that manual are 986551 and 986636 for the install packages.
https://www.flickr.com/photos/advance-design_parts_co/8129416019/in/set-72157631868452754
Here is another number to search for as well.
https://www.flickr.com/photos/advance-design_parts_co/8129328270/in/set-72157631868452754

1950 Chevrolet 3/4-Ton 3600
More pictures on Flickr