The original strips have a dimpled recess for the screw head, no washers. Here is another view of the correct bracket as shown in the previous post.
https://www.flickr.com/photos/advance-design_parts_co/34278894970/in/album-72157631868452754/
A factory view, interesting that some come pre-drilled for the mirror and others do not, this view from ‘47 shows the larger hole.
https://www.flickr.com/photos/advance-design_parts_co/17037319947/in/album-72157651718017649/
In this view from ‘51 the hole is gone, I believe these holes were phased out in early ‘49 and thus the bracket became a requirement for installation.
https://www.flickr.com/photos/advance-design_parts_co/8258512740/in/album-72157632208362076/
Inner trim piece removed from a ‘49 vintage showing the mirror hole.
https://www.flickr.com/photos/advance-design_parts_co/11590024186/in/album-72157631868452754/
Complete trim set from a ‘52 vintage truck, no mirror hole.
https://www.flickr.com/photos/advance-design_parts_co/11593840945/in/album-72157631868452754/