Global Mapper v24.0

Custom NAD83 Datum with Clarke 1866 Spheroid

partjohnner Global Mapper UserTrusted User
Is there any built-in version of the NAD83 datum which has an embedded "Clarke 1866" spheroid? If not, what parameters do I need to enter if defining a new datum ("Create New Datum") which would associate the Clarke 1866 spheriod with the otherwise normal parameters of NAD83?  The reason I am asking this is that I am trying to sync GIS data with a data set that was built with the following parameters:

  <entry name='UTMZone12NorthNAD27_HillCountyMT'>
    <structure type='ProjectionUTM'>
      <entry name='datum'>
      <entry name='ellipsoid'>
        <value>Clarke 1866</value>
       <entry name='name'>
      <entry name='originLatitude'>
      <entry name='originLongitude'>
      <entry name='originX'>
      <entry name='originY'>
      <entry name='scaleReduction'>

As far as I can tell, this specification seems to be using all of the components of the NAD83 datum except for the older spheroid/ellipsoid.  In a custom datum pictured, I am not having luck only specifying the Ellipsoid as "Clarke 1866" -- there is probably something else I need to do to "recreate" the fundamentals of the NAD83 datum.

Any assistance would be appreciated.