My solution to such a problem, trying to keep a gun as original as possible: I carefully remove the unuseable original bases and store them away to be able to put them back on for collector's purposes. then I file bases, fi Warne style, from some steel and fit them into the original recesses. Now I am able to mount any modern or vintage scope with available rings. As an example, here is a pre-WW1 Voigdlaender 3x long eye-relief scope mounted with available semi-modern rings on my Haenel M1900, likely in the original position.