I think I can cobble together a jig to hold the upper casting on a drill press in the right orientation. I think 1/4” of adjustment is all that will be required. Drill one hole next to the current hole and then use the drill bit like an end mill to create the slot. Of course this will not solve other worn parts but it will allow a bit of adjustment. If I get the ambition I’m going to try this on an old set of upper castings I have.