Posted this picture on another site and thought I should also post it here to help others
On 69-70 Shelbys the attaching bracket welded to the front bumper was blacked out in an effort to make it less visible.
Suggests it was applied with a brush and likely has flattened IMHO with age. I've redone them with a semi-gloss. Applied just short of where the bracket and bumper meet on this example
Here is a picture of an unrestored front bumper and the blacked out attaching brackets
Sorry the area is not well lite and the contrast is not as great as I would like but hope this helps