I would not consider myself an expert but I have collected CW relics off/on for over 35 years. There are primarily 2 types of plates that you will see. The older version is what collectors refer to as the "puppy paw" clips that one of the other posters put in their answer and the 2nd pattern which you seem to have found a representation of the "arrow hook" clips. The puppy paw version was made primarily made before the war started and the arrow version was more prevalent after the war began. Both are found in substantial quantities. CW buckles and buttons will turn up at parks and old homesites because the old soldiers lost them at their post war homes and local G.A.R. gatherings over the years. Concerning your buckle. The arrow hooks look right in my opinion, the lead does not seem to be overfilled yet it is difficult to tell by the bend your plate has in it. The only concern is the 3rd clip that went into the belt hole. traditionally those are rather beveled as someone mentioned. Does that mean its a repro? No not necessarily. There were a variety of manufacturer's during the war so there is a variety of original plates out there with different backs. My recommendation would be to reach out to a Civil War relic dealer, someone who sees these plated every day and get their 2 cents. If you mention your are thinking about selling it but are unsure if it is authentic or not they will be more inclined to assist you as they need new merchandise all of the time and they buy from diggers. I would reach out to Larry Hicklin with Middle Tennessee Civil War Relics or Rafael Eldrige with Shiloh Civil War Relics...see their website links below.
With the new pictures, where you can see things more clearly, I am inclined to think that it is authentic. I have sent a request to Pete to chime in to give his thought on it.