This 390 build sheet (different car) was posted on VMF, the box "B-4" indicating a "GT" model is not checked. I believe the car is not a GT car.
Supported by owner's comments "When I bought the car in 1981 is came with std-Rear Valance, left and right "390" ponies and std Mustang pop-open gas cap (
no GT badges)
Interestingly, I responded to the post. I apologize for being a dickhead in my younger years
So, I think there was a possibility of getting the chrome parts on a non-GT. I also think The C8OF-B (blue lid) was also available
I guess there is some possibility that the C8OF-B is something other a non chrome air cleaner?