Hey Stan,
The insert for the 73 rear bumper guard is a one-year-only part. (Ford part number D3ZZ-17A807-A Engineering ID# D3ZB-17A807-AA).
The '73 Cougar did not have rear bumper guards, eliminating an additional source for the inserts. Since the rear bumper guards and the deluxe bumper group (which included the same bumper guards) were not standard, that also narrows the supply source even more.
There is a reproduction by Daniel Carpenter Reproductions. How well it fits is anyone's guess. Fellow forum member/vendor Don
@OMS does show a set of those.
https://www.ohiomustang.com/store/order_page.asp?itemid=506
I rechecked NPD, and while they show the horizontal inserts for the deluxe bumper group, surprisingly, none for the rear guards. I saw where they offer an insert for the front, which is incorrect since no front bumper guards were production installed on any '73 Mustang.
There is a site I check for NOS parts that shows a few of these inserts at different vendors.
https://www.rearcounter.com/D3ZZ-17A807-A-parts66431.html
Understandably, the sellers are aware of the discontent with repo parts and the desire for original Ford parts, so occasionally the prices reflect that. There are contact phone numbers and pricing request options. If the prices you are quoted are on the outrageous scale, the $19.95 price at OMS (Ohio Mustang Supply) may make it worthwhile taking a chance on the repo's fitment.
At least now you have some options. Please let us know how this turns out.
