Your Gilbarco air meter was either introduced in 1936 or 1941 depending on which one it is.
I wrote and self published a book on air meters (TIREFLATORS) in 1996, in which I identified 170 air meters made since 1896. Since that time I have identified another 275 air meters for a total now of 450. My hope is that the same publisher that published my Gas Pump Identification book will published a similiar book on air meters. I am working on the images now.
My book is still available (very limited copies left). For more information see my website:
www.crspub.com You can go directly the book at:
http://crspub.com/tireflator/books.htm Jack Sim