Here is the manual , I found a 66 and 3C models at the google , same or not , I dont know the brand name of the shutter also. Tell us what is written for the producer of the shutter ? And if there is a shutter serial number , give it to us also , Someone with a 50s catalogs could help.
Here are the wonderful sites , bottom ones are for idea also.
Welcome to APUG and good luck , send some photos during repair and someone would like to help you.