Back in the 80's, I was fortunate enough to pick up at a Swap Meet, a 1967 Autolite Registered Dealer's 3-Ring, indexed Binder which covered the majority of the Autolite products available at that time. So, I went there first to see if I could get an answer to the Applications of the AT6. In the Spark Plug Section, first there is a 4-page, light cardboard folder showing common applications. The first 2 pages cover American Passenger Cars, page 3 is Imported Passenger Cars, and the last page is Light Trucks. It was not until the last page that the AT6 appeared (copy attached). Following this 4 page folder, is a 56 page booklet covering more detailed Applications, Service, and Sales. In the detailed Applications section, there are many, many more. The additional include some trucks and busses, Tractors, Lawn Tractors, Generators, Contractors' equipment, etc., etc.
A real key here is that the "A" designates a 14mm Spark Plug, not an 18mm as most all Fords were. I have attached, for information, the last page of this booklet which is "Identifying Autolite Spark Plugs".
Hope this helps.
Bob