Thanks Kerry, I believe those rivets are in line with the service bulletin Jeff posted on pg.1 of this thread. Yours being built AFTER the October date implies it was done at factory, not the dealership. My thoughts are, also considering your build date, that the 68's were different to a degree, even in the earlier than the October date mentioned, like so many other things, to that of the 67, or early 67 design. Once again this thread goes into the "til we have more original examples" category, but it does follow the O.P.'s original lines of questioning before I steered it away asking about 67's.
About the only other question I might have on your car is, if you look from UNDER the drip rail, are there any rivets along the edge of the window weatherstrip channel? Chances are, the answer is "NO". But on the odd chance that it DOES, it would be good to see a photograph of those rivets.
Thanks very much again for adding your pictures. It surely will be help to others.
Richard