Didn't find John Lorrance or Mattie, but found a Nannie Lorance who filed a MS CS Widow's Pension Application in Hinds County, MS, in 1916. She stated that her husband was Mort Lorance, who was in the "28th Regt." This unit would almost certainly be the 28th MS Cavalry, as the 28th MS Infantry was almost immediately transformed into the 28th MS Cavalry after formation.
I also find an "M. Annie Lawrence," who filed a similar pension application in 1916 in Walthall County. She said her husband was John H. Lawrence of the 14th MS Cavalry.
Hope this helps! -- Jim Huffman, Gainesville Vols