Determine the year from the serial #, then find (online) the catalog scan for that year. Not sure if the catalog covers all models, also there were customer determined options available I think.
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1989 Schwinn Paramount OS
1980 Mclean/Silk Hope Sport Touring
1983 Bianchi pista
1976 Fuji Feather track
1979 raleigh track
"I've consulted my sources and I'm pretty sure your derailleur does not exist"