Bummer about the CMM , but it would only tell you that you have a problem , you will know that once you have the saddle fit . OK quick and dirty . On a caliper , fit two diameters I would groove two pieces of round stock and hold them in place with a set screw on the caliper jaws . Set "0" and measure away . Those measurements will only differ at most .0005 , will that be good enough ? Maybe hi spot blue and stone down .? For your last question , that sounds right and no I don't think you are over thinking it . I think you have a good handle on it .