Jack's site has a lot of gas pump and air meter information available. You should visit there.
The Gilbarco 996 was made from 1947 to 1955, according to Jack's book, Illustrated Guide to Gas Pumps. There is an old Blue Book of gas pump production where one can look up the year produced according to the serial number. If you posted the serial number here, you could get the year if a member would look it up in their book. A picture posted here will usually get you the make & model identification provided by one of the many knowledgeable gas pump enthusiasts who are members of this forum.