Seems most Z11s I have seen have rear bumper guards. Mine didn't have a rear bumper when I bought it - so I've always had an OEM with the bumperets on it. Curious what was standard on these and if bumper guards were optional if there's a way to tell if it was included on this one originally. I believe this one had a Endura bumper on it originaly as there was a rusted out one included with the parts when I bought it back in 84, don't know if that matters for the rear of how to tell if it was original either.
The bumper brackets for endura bumpers are different than the brackets for the chrome bumpers . Did you have all the pieces to mount the endura bumper when you got the car?