In one of his books on single shot rifles, Frank de Haas wrote of changing the length of the connecting link in a Ballard by drilling and tapping a hole in the bearing surface of the link and fitting a set screw in the hole, so that the surface of the set screw (not the adjustment end, of course) became the adjustable bearing surface.  Perhaps something like that would work.

I think you have to be one of the anointed to get any help from the Winchester Collectors forum.