I might be able to help. Can you get the serial number? It should begin with C or J. After the first letter, the next digit is the year it was made - you'll need to know the decade. In your case you would assume it's the 70s. The next two numbers are the week of the year. The final 5 digits are the unit number. The washer I bought new in 1986 starts at C632, meaning it was made in Clyde, Ohio, 1986, 32nd week. If you think your washer is from 77/78, its number should start as C or J (J is for the old plant in St. Joseph Michigan), then have a 7 or 8 followed by a week number from 01 to 52.
I hope that helps!