Block out of square

^^^ LOL. Well, actually, I straightened out a pretty baldly warped /6 exhaust manifold 2 years ago with a belt sander; took my time and kept checking with a known rigid straight edge (checked to be to under .001 over 2'). (The process of grinding that way does not seem any different that a blanchard grinder.) And lathe ways get trued up by hand scraping. I've done other mods by hand methods. It is not a .0005" accuracy method, but you don't need that here. Gotta go gradually and not overheat the metal. Certainly doable if you want to trade time for $$; not any worse than shims IMHO.