I am positive that the very early 66 Merc I had in the 90's had a cowl tag on it just like this truck. Maybe it only got one if it was a 6 character DSO?

From 1946 to 1965 all Mercury trucks on the warranty plate were identified as a Mercury. These plates do NOT look like the American warranty plates. In 1966 the auto PAC agreement was in place and the Mercury truck was phased out by 1968. In 1966 FoMoCo declared all warranty plates had to coincide with the American made plates and subsequent codes. Therefore there is limited ability to prove if a truck in 1966 was born a Ford or Mercury. The definitive proof is the registration and also to a large degree the DSO. A DSO that starts with the letter A designates a Lincoln Mercury dealer whereas the letter B designates a Ford dealer. There have been some reported cases of a Ford dealer delivering a Mercury truck to remote regions of the Yukon or N.W.T. Marti reports are from 1967 to 2002 only thus making a 1966 the most challenging truck to identify . We are hoping that no one simply bolted on the Mercury pieces in place of the Ford pieces.

RMM