I have a Lt. Henry Gray in my family and my uncle has his portrait on his wall. Lt. Henry Gray (1824-1883) served in the Manchester Irish Rifle Volunteers between 1859-1864. He and his family lived in Salford having left Bangor Co. Down, Ireland around 1855. He was presented the portrait by a Captain John Porteous and a number of other volunteer friends. From what I read above, it sounds like the same individual.
The picture can full text can be seen here:http://www.graytrees.com/LtHenrygraypic.html