I didn't see a link in the main 67 SJ running change thread:
http://www.concoursmustang.com/forum/index.php?topic=20681.0and wonder if this is indeed a running change or a stock/restock assembly line issue.
On my signature 67 SJ car I thought it had the large head screw on the valance, but my original valance shows only a scuff mark for the smaller screw (see pic).
If your valance has the correct stamping date for your car (similar to other sheet metal dates, but before your actual build) don't go by what is installed today. Instead look for screw witness marks on the valance under the screw.
My valance is 12/8/66 on a car with a lot of mid-January sheet metal. It could be that the dual exhaust cutout valance wasn't in high demand, so early stock may be expected.
This un-restored car:
http://www.concoursmustang.com/forum/index.php?topic=17981.0shows the small painted screw in the third hole in from the outside.
67gtasanjose [Richard] noted "Sticking only with San Jose built 67's, I know my November-built example used a flat screw head (similar to the screws found under the upper door weatherstrip holding the stainless trim to the roof rail)." in this post:
http://www.concoursmustang.com/forum/index.php?topic=17981.msg118069#msg118069I think we need a survey on this item.