Thanks for the notes, everyone. I went through the LOC site for quite a while but could not find a match. The size is something closer to 4 inches by 5.25 inches - sorry for not including that info. The 627 Penn Ave gallery did not open until 1868, but I am not sure if that necessarily means that the image was captured post-war. The 627 Penn Ave gallery closed around 1880. I am assuming the photo is closer to 1868 since I think CDV's were falling out of favor possibly even before 1870. The vexing thing is that it looks for all the world like a Union general but I have not been able to match it to anyone. There were not that many Major Generals roaming the countryside back in the day!
Edit: Sorry JNanian - I did not see your post before I posted this one!