There was something about those two Sharps rifles that ran a bell in the cotton wool fuzziness that is my mind. I didn't recognise your 'Monika' MS64. Then I saw the name Leon and Netherlands and everything fell into place. We have been in touch before back in about 2005 or 6 and you were very, very helpful to me then. Like Chuck I won't tell you how to do any work either your far more skilled than I'll ever be. Can I take it that the numerals on the Long Range Staff were CNC engraved? I can spot only two very minor differences between your Staff and the original Borchardt Long Range Site other than for the rotating eye disk you mentioned.
I wish I could be more helpful with plans for the 1875 but I'm really stuck for a lead. Sorry.
Harry