"G.J. Buchanan" appears on the on-line NPS roster of Soldiers and Sailors as "adjutant" (Field & Staff) of Thomas H. Johnston's 1st Mississippi Infantry (M232 r5).
Might this be the same man I hold in the Signal Corps as a sgt under Lt. Duvall (Capt. Manning; Longstreet)? I'm trying to get a handle on him for further research, and this thin reed keeps attracting me. He was with Duvall at Gettysburg, but not on a signal corps roster of circa Nov-Dec 1864. The usual problem when no first name is known, nor place of origin.