The windshield divider on the 1947-1948 and some of the early 1949 model advance design trucks were drilled for the inside mirrors about 3 inches from the top (I have seen a couple of these on parts trucks I have had). Those trucks had a threaded plug installed in them. The bracket offered by many of the vendors is the other alternative. Here is a photo of the divider mentioned above from an early 49' GMC.
https://www.flickr.com/photos/advance-design_parts_co/11590024186/in/set-72157631868452754
Here is a comparison set-up without the mirror hole.
https://www.flickr.com/photos/advance-design_parts_co/11593840945/in/set-
72157631868452754
Another early 49' l had with a mirror installed in the location mentioned.
https://www.flickr.com/photos/advance-design_parts_co/8130452603/in/set-72157631870734114
An early 49' Chevy example.
https://www.flickr.com/photos/advance-design_parts_co/8130475544/in/set-72157631870734114
I didn't get more detail photos on these two trucks because I did not part them but resold them as found.

Last edited by Brad Allen; 12/26/2014 5:03 AM.