Sorry for the late reply--I just remembered to go out and check, and my '62 Suburban has sheet metal screws holding the tail light lenses in.
I believe these to be original, as I've pulled another set of lenses off a junkyard Suburban and they also had sheetmetal screws, and the spare tail light housings I have from Ebay don't have any kind of boss, screw or anything with enough metal to support machine screw threads.
-Brad
