I recently saw two "Westminster" releases in series I have not seen before (or don't remember).
  Can anyone provide some background on them, when they were active, how extensive was
the catalog, new recordings or reissues, etc.
  The labels are WESTMINSTER ABC, and MCA WESTMINSTER.
  I am aware of the two-tone orange cover series - these are NOT that series.

The Westminster ABC release appears to have been available in mono and stereo, carries
catalog numbers XWN/WST 17135 Norman Treigle - arias, recorded June 1967.

The MCA Westminster release MCA 1401  Walton: Facade, Gingold, Oberlin.  Copyright 1980.

Thanks!
Best wishes, Thomas.