Pretty sure these two are original on these REAR guards!
I bought the ones from NPD and put them on my car even if they are incorrect.
The presumed purpose is to keep very minor collisions at the guards from causing the bumper to need replacing ANNND to keep wrecker-tows from damaging the chrome.
Remember, Mustang was ONE OF, if not THE first car to use a painted body part beneath the bumper. Tow Trucks, known as wreckers here in the south, could no longer
just pick up the front end with a hook. They now had to have 2 wide rubber straps on a frame apparatus that rested against the bumper and bumper guards. Two chains with huge hooks
reached up under the car and pulled the front end into firm contact with the two rubber strips. This protected the painted lower valence panel.
The OEM bumper guards had a plate with a tiny hole, welded into the upper tip. The rubber bumpers fit right in that area and a rubber teat pulls through that hole.
I see the "vintage" tow truck (aka wreckers from South of the Mason-Dixon line) is equipped with Early-American rust.
A bit off-topic, but I looked at a rear bumper guard I have on the shelf and it has the provisions for the rubber bumper (p/n 379944-S). Also note, there is a difference between 64-65 and 66 locations of the padded nutclip (p/n 378960-S2) on the rear bumper guards shown in your picture, 64-65 on the bottom, on the top in 66.
Back to topic, sort of; 64-65 front bumper guards are documented to use a round rubber bumper (377769-S, Assy Man AM0001 pg8 item T, and AM0006 pg8 item T, part dwg on Ford Standard and Utility Parts, 1965 pg29) while 66 (also 67) use the triangle rubber bumper front and rear (379944-S, part dwg on Ford Standard and Utility Parts, 1966 pg29).
The Ford Car Parts manual, sect176 pg40 & 42, indicates the service front bumper guards are
"less pad" and a rubber bumper, 379944-S, ordered seperately for front and rear, but a quantiy required of 8. Only one per bumper guard is documented or provided for with a hole, so the qty is off.
Jeff - note above
"less pad", the source of the original question?
Jim