Great! Thanks. This is what I thought, but all kinds of conflicting data out there and the original paper work is long gone as is the original owner in 1984 (my dad).
All 61K serial numbers were issued in 1980, so armorer951's answer is correct.
One should exercise caution, however, when relying entirely on the SCSW for serial numbers in the xK and xxK ranges. They are not always correct, being mere approximations. That is not a criticism of Supica and Nahas, BTW. They could only go by the information they had available.