In 1931, Ford introduced the special rustless (stainless) steel radiator shell AA-8200-B for use on some deluxe Model AA trucks such as the AA Deluxe Delivery and Ambulances.
This shell is designed to fit the thicker 4 row radiator used on AA trucks and is not interchangeable with any Model A passenger or commercial shells. It is interchangeable with the black painted steel radiator shell typically used on 1930-31 Model AA's.
Note the horizontal line of the upper radiator opening frame, as well as the unique stamping shape of the lower panel, compared to a typical Model A radiator shell.
This stainless shell came from an AA ambulance and has an interesting red Ford emblem. The July 1931 Ford parts catalog shows a unique AA-8242 emblem for use with the stainless AA shell, but I don't believe it is this red one.