Let's start with some things that might be helpful:
I would not rely on the Marti report, they often have omissions.
If your car was equipped with rear bumpettes in 1968 it would have the rubber strips. It would also have some conical rubber cones on the back side. The bumper guards are painted body color.
You stated you have a Metuchen (MEH-2-chen) car. Then you should have the "RB" code on your build tag, located by the passenger side hood hinge. It will also be on your build sheet. That will be found taped to the main wiring harness, behind the dash.