The scrollwork bears all of the characteristics of a Japanese trained engraver. Many such guns were purchased by GI's stationed in Japan. They were bought through the BX/PX and engraved by one of a few local engravers who catered to the GI's. Also during the 1970's - 1980's there were a few Japanese engravers who worked in the US. A couple worked for REI Engraving in Illinois and Sam Kinamuchi worked for Ken Eyster in Dayton, Ohio.
I have never been able to distinguish the work of one Japanese engraver from another, however, most done in Japan used silver wire inlay and figures and the ones done in the US usually had gold inlay, if any.