Actually I mis-directed you in referring to the parts catalog for a part number. Though it is in the book filed under it's group number and section number, it is a royal pain to find.
The easiest path is to look in the Assembly manual if it is a part that is assembled to the body on the assembly line, though I think it is most likely part of the car body when Chevrolet bought it from Fisher Body. As such the part number would be in the Fisher Body Service Repair manual under the chapter on doors. The Fisher Body Service Repair manual is more for body men doing collision repair it still shows all of the parts and how they go together.
The Assembly manual shows how the car was assembled part by part with every part listed by part number and description and every fasteners torque specified as well as any adhesives or other chemicals call out by GM part number to put the car together.
If you are going to work on these cars you will need four basic GM manuals (they were published by Helm) the two I have talked about above, and the Service Manual that describes overhaul procedures for the drive train, and the Chassis Service manual that out lines how to remove and replace all of the parts of the running gear (front end parts, brakes, shocks etc.) that wear out.
All of these books have been scanned and digitized to be sold as an image on a CD; though I much prefer an original paper manual that was originally given to a Chevrolet service technician the year the car was new. That tech had to have kept it all these years in order for you to buy his copy from his widow upon his demise as I can not imagine him parting with it otherwise. I know I'm not selling my manuals: though My Widow can't wait until I'm gone to get rid of them, I'll bet.
Big Dave