I used to collect boss pedals. AFAIK, all silver screwed MIJ boss pedals have their serial number stamped within the battery compartment. it's next to the switch if I remember correctly.
The components is SLIGHTLY different between the Japan made boss pedals. However, the main board is the same. do note that every board has a "code" to tell you which version is it.
If you know your pedal is made in 1979, than yes it should be silver screw.