Japan was/is not a member of Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives (CIP)
A gun intended for the U.S. market would not require CIP proof markings ie. the fleur-de-lys.

I tried to find some images of other Kasuga action flats without success.

I think (an opinion which is worth nothing) that "Steel" means steel shot compatible IF the chokes are steel shot compatible.