Thanks Bob. Zinc dichromate, makes good sense, they would be less likely to rust. Funny thing, I saw another Shelby just last night and noticed the valance screws were shiny. I thought to myself that this guy got it wrong, but I stand corrected. Zinc Dichromate it is then.
However, I agree with Jeff when he says that Mustang valance was in place (at least for my car) when they applied the body color. We found body color over spray at both far ends applied on the light grey primer. We also noticed two round spots of yellow paint. What is that? we thought. Yes! That's the body color that came through the backup light hole on the valence. The yellow circles can be seen at lower right of the picture, I included. I will also include the other side. The passenger side looks more as if it was masked, I dont know. But the backup light hole overspray is also seen. All this detail and the back end of the valance had been covered in sounddeadner or undercoating. Quite messy but it kept the back end pristine.