Trying to remove door locks, 72 Duster?

I have had to remove a million of these things when I had a locksmith biz. Some cars were rustproofed, and factory applied sound deadening often cements these clips in place causing them to resist one’s advances.
Easiest method to remove and reinstall “C” clip securing door lock cylinder is a pair of small vice grips. You can put a little English on the damn thing, it won’t get away from you dropping to the bottom of door, and you won’t bust up your knuckles on raw sheet metal edges when a screwdriver or other plier slips.