Re: diffrence between Selmer Paris and New York
If it's 63K, then it was made in Paris. The NY-Elkhart-London just reflects their global distributorship at that time (late 1950s). Some early Mark VIs had Mark VI clearly engraved on the back of the body, above the left thumb rest, but later ones did not. However, most that I've seen are marked Mark VI on the bow-to-body brace. In any event, it's a Paris horn, and if it sounds great, you're in business! Experiment with different mouthpieces to correct intonation issues, perhaps a larger-chamber piece would help, especially with upper-register sharpness. If that doesn't do it, have an experienced repair technician check the key heights, and make sure the correct thickness of pad has been used on the horn.