Hey Robert,
Yes, it is a custom coordinate system for a local mine grid. It's based on a NAD27 datum and the Clarke 1866 spheroid with adjusted false eastings and northings, etc...
We have a GP function that allows the user to enter a local coordinate and return the location on the map (web mercator), but I'd like to do the reverse now where the user could pick a point on the map and have the local coordinates returned. I'm sure I could create another GP tool to do this, but I hoping to use something like the eLocate or Coordinate widgets.
Warren