I have the Ford Accessories (Muscle Parts) literature from that time period, and it does list the Cobra valve covers as a dealer available OTC dress up item.
Yes, not concours stock, but still a Ford originated optional part. So if you cannot find the originals, I would think you are still in the Ford family.
Just my .02
Added edit - If this was the case, would those be original COBRA vc's? Part number or casting date?