Dee: I couldn't find anything for a Cpl. E. A. Briggs, esp. in the Jeff Davis Legion Cavalry. I checked a database of all CSA soldiers and "Horsemen of the Jeff Davis Legion; The expanded Roster of the Men and Officers of the Jeff Davis Legion, Cavalry".
I found a Corporal Eugene Briggs, "H" Co. MS 48th Infantry;
and Private Eugene Briggs, "H" Co. MS 2nd Bn St Troops Infantry (same person).