Mark:
I have had the same problem as Duane in the past and since it cost me a lot of work once I go the way I know works which is the same as Duane's. My logic is, I don't really care where a tool maker put something relative to a ball. I care where it is relative to the PCS. It sounds as if you work in a tool shop so I don't think my logic could apply to you very well except maybe instead of establishing bushing and block locations from the sphere's try doing the exact opposite. I measure sand casted parts now and have also found repeating a DCC alignment at least twice before measuring features I tend to repeat within a micron or two. It might help to give it a try. It can not get any worse than it is now.

Best regards,

Terry W. Prather