I was just finding a pic to answer a friends question on park light mounting when I remembered this question and it has me stumped.
Where the nosecone slips in above and below the park lights there is a fastener hole in the top of the skin that holds it up and onto the inside of the steel bumper cutout lip. I think it's only at the top. Mine never had anything there so I added plastic trim fasteners and pushed them in 15 years ago. But what was there originally?
Front bumper before park light plugs by
Aus78Formula, on Flickr
You can see the black bumper skin in this one and hole in bumper.
78 front bumper inside 2 by
Aus78Formula, on Flickr