It is possible. Looks like a Biwa set in gold. But If it was in the 1960's...from Japan, I would guess it would be set in Sterling or Silver. It looks later or not from Japan? BUT....many vendors from around the world set up in the Airforce Base Exchanges and it could have been originally another country with a stand at the Base Exchange. Also a jeweler using Japanese Pearls could have made it for your grandfather...at the Base exchange, that happens too. (This was happening even during WWII.)