On the 1999 reissue of Meet The Temptations the notes say that the album was originally released in March 1964 and "subsequently remixed and released in Stereo in 1966".

The 1999 CD is certainly the stereo mix.

Has the original mono mix of this album ever been released on CD?

If not, this would be a great place to start for an "Expanded Edition" program for The Temptations on physical CDs. All 50-plus albums!