I am hopeful someone else with a 53 may chime in as to factory fit, but I have seen at least a couple of 53 trucks that have a fender mounted small non-trumpet horn. This makes sense with the accessory horn being one mounted to the firewall? Here is a picture of a 53' I owned with this horn.
http://www.flickr.com/photos/advance-design_parts_co/8130447759/in/set-72157631870734114