I looked up some Oklahoma Historical photos online, and saw examples of all of the light combinations I mentioned above, plus a couple of pictures of trucks with 4 clearance lights evenly spaced across the top. So take your pick Materman.

Spanky Hardy
Collector Of Fine Old G.M. COE Trucks & Antique Holmes Wreckers

1948 Chevrolet 5700 COE Holmes HD W35 Wrecker
In the Stovebolt Gallery
More pictures on Photobucket

1950 GMC 250 1-Ton
In the Stovebolt Gallery