To answer Glowe's question , yes I have had the stocks off and they are marked with the serial number on the RH side. Another part of the mystery of this gun is that the serial number has been moved from the bottom of the grip and stamped in small numbers on the side of the frame under the stock. The bottom of the grip now has this OTTO B. 50 stamped across it. I'm thinking that was done by whoever acquired the gun from its Japanese source ? The gun is also marked on the frame, cylinder, and barrel assembly with a small GG6 which should be assembly numbers I think.
A lot of good input from you folks. It will likely take me a bit of time to absorb, and due to very poor health, that at times puts me in bed for numbers of days, please except my apology if my follow up is or gets slow. Thanks again to all, and keep whatever thoughts you might have coming

Keith