More original (unpublished) underhood Mustang photos from the shoot might certainly tell the story.
Found some research from the Group 2 FB page: Based on the '67 team Shelby car, I now strongly suspect it's an oil catch can. Maybe not the plastic bottle version seen in the photo, but the same function.
Found some research from the Group 2 FB page: Based on the '67 team Shelby car, I now strongly suspect it's an oil catch can. Maybe not the plastic bottle version seen in the photo, but the same function.