[Kube]

There is in fact a definitive answer. The rear bumper was optional. The rear bars as the original poster had surmised are different than the passenger car.
The bumper bar for the front is the same as the passenger car, either front or rear.
The rear bumper bar for the PU is unique. It has much less of a contour than the passenger car version and the spacing for the bumper bolts are different as well.
Under no circumstance were bumper guards (bumperettes) installed on the rear.

There was a guy on eBay about six weeks ago that was advertising the bar and irons for $50. He had them listed very incorrectly. He would not ship. Wouldn't even consider it.

The eBay listing has ended but I did manage to find it. The seller is ELVIS43. The item number was 357134618275. You can find this doing an "advanced search".
I see now that he had changed the ad to show what it really is after I had told him.
Perhaps you can talk him into shipping it. Or, he has offered to deliver to Hershey.