They were used to tie down the rear of the car when being transported by the car haulers. They are bolted to the rear frame rails near the mufflers. Some dealers removed them and some did not. I have a picture somewhere if I can find it.
I have a Broadcast Sheet for a 1971 Challenger. If this is your car send me verification of ownership, and I will send it to you.
VIN JH23G1B202954.
As you can see that fourth digit is faded and only the top is visible. By the shape of it I believe it to be a 9 rather than an 8.
E44 - 318...