You can search Hank's Truck Picture's for idea's.
http://www.hankstruckpictures.com/trucks.htm Hope this help's, lot's of old picture's to chose from.
These link's are probably what you are looking for.
http://www.ttacparts.com/reddot.html http://www.heco.net/rd_rooftop.htm may have to click for picture's to appear.
Later, Neil#2 aka doodlebug.