I have a pair of original Stevens tang sights. They are generally similar, however, the threaded elevation shaft differs on both.
One is short and one is long.  Neither will allow the total use of the graduated scale on the side of the vertical slide.  The short one allows the aperture to utilize the lower part of the scale, but runs out about mid scale.  The longer one allows the aperture to reach the top of the scale, but only lowers it about mid scale.
Neither threaded shaft appears to have been modified.
I don't have much history stuff on Stevens sights; anyone familiar with them and can shed light on the differences?  Seems odd neither set up allows total use of the vertical scale.
Thanks!,
Mike.