An AD series (Advanced Design) truck goes from 47 second series to 55 first series. So, yes, you have an AD series truck. The trucks before the AD's were nicknamed the Art Deco's and the trucks after were called the Task Force trucks. Hope that helps some, welcome to the Stovebolt,
Scott

Scott Ward

2 1948 1.5-ton Loadmasters
The red one and The snow pusher
1 1950 3100
1 1955.1 Chevy 6500
1 1954 Chevy 6500 2-Ton
1 1955 1st Series COE 5700
1 1963 K20 (454)
1 1964 C10 (350)
1 1951 1.5-ton Dump Truck
1953 and a 1956 Ford F800

Raising a teenager is like trying to nail Jello to a tree!