That is a draw-tite part number according to this site:
http://www.etrailer.com/hitch-1963_Chevrolet_Pickup%20with%208%20ft.%20Bed.htm Interestingly, if you go to the instructions page it says "Towing Products, Plymouth, MI", which may or may not be associated with Draw-Tite. Probably Hidden-hitch and Drawtite are brandnames of the same parent co.
No affiliation, but I have ordered lots of stuff from etrailer.com and they are fast and accurate....
