Hi Bill
You maybe right about the horn placement further to the left side from what mine show, from memory I thought the air horns were near the edge, was somewhat surprised that they were just left of the drivers head. The remains of the two trucks that I have may have had dealer installed air horns and did not come from the factory that way.
My son is holding many old pictures of our company trucks from the 60's, hope to place them on webshots soon. Several of them will show air horns. I'll also check and see what brand name they are. As far as Scott's truck goes the horns would look correct mounted either just left of the driver's head or to the far left of the driver's position, never to the center of the cab.
I appreciate your thoughts on the matter.
James