Suggestion...first try to find a descendant of your gr-gr-uncle, it could be priceless to them!
Next suggestion would be a Civil War Museum either where he was from, or in the areas mentioned where he fought.
One of the saddest things I have seen was an 1865 Bible at an auction that I bid on to try to reunite it with a descendant, but was overbid by a woman from Korea who purchased it to take the pages apart and sell them online as decorattions. I continued to research the family names in the Bible, and their only child died as an infant, so there was no direct descendants after all. That was some consulation to me. The Bible had a section that was what I would describe as a photo album, complete with photos, one of a sleeping babe. That photo was actually the funeral photo of their only child.