Initially distributed alphabetically. Have you ever tried calling GM for assistance, no help with old info. NCRS's Chevy Muscle Docs division has the database and microfiche from GM archives and manages the information at a charge of course. The person I am working with already sent the VIN into them and they came back with zone 44 dealer 160, thought to be Gordon Chev etc. but of course it couldn't be because it's a 66 car and Gordon opened in 83, hence the search goes on.
Paul