Seems to me that you are probably right! The Japanese have always been artisans --- so they may have copied the boxlock. At any rate the SKB guns and Mirokus of the seventies were the bargains of the century. A few years ago I saw a lovely 12 ga.
SKB with straight grip, splinter forend,swamped rib, lovely colored case hardening, marked "Royal". Was told it was made for the european market. Thanks for the input. Chops