I wonder if there was any difference between weight divisions on trucks?
i.e. The heavier rated trucks didn't have an interior mirror due to the fact some would have bulkheads/box bodies behind the cabs,therefor rendering a mirror useless?
Just a thought....

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.