I don't know where I got the notion it was Texas General James Harrison. He had only just returned from Richmond in Feb 1865 and was between commands. His next command assignment is as follows:
3/16/65 Houston/ S O #75/III-Brig Gen James E. Harrison will proceed to Huntsville, Nacogdoches, or wherever the Brigade lately known as "King's Brigade" may be found; will take command of said Brigade & move it without delay to Houston.
I believe Fay is actually referring to Col I F Harrison commanding a Brigade of Louisiana Cavalry.
Thank you so much, I owe you one.