Sharpening Stone Set (Large & Small) - King - Showa Era - Rare Item

Found in the box of my grandfather, who ran a cutlery shop and passed away in 1969.

Two whetstones, large and small, with King stamped on the surface.
Could these be early King whetstones?

These are vintage items that have been stored for over 60 years.
There are scratches, scuffs, dirt, and chips.
Please understand and agree to the condition of these vintage items before purchasing.

Thank you for looking.