Well... I have looked at the Boss half a dozen times. It is really unique, no doubt about it.
The profile of the upper barrel has nothing to do with the smooth curve you can see in the Merkel.I cannot say anything about engravings. Not one in sight. In my humble opinion, if used by an unknown gunsmith, the design of the method used to attach the scope to the gun would make scream all of you.Maybe the mounting system is not original. Nothing to do compared with a Suhler claw mount.
Next time I want a custom chopper motorcycle, I will ask Rolls Royce to make a project for me. It will also be unique.
In Spain we have a saying: "Para los gustos se hicieron los colores", very similar to "Beauty is in the eye of the beholder".
200K. Virgen Santísima.