I had a load of uncles and cousins in Co.I of the 18th.Tx cavalry. The Company was mostly from the part of Kaufman Co.that is now Rockwall. I cannot think of the author now,but the book,"Band of Brothers," will give you a lot of good info on the regiment and the brigade and has a roster of most of the soldiers.
The picture looks familiar.Send or take a copy to the Confederate Research Center at Hillsboro for ID.This saturday is the big Symposium down there.Im sure you will eventualy track it down.
MWT