Well, it's not a 1861, it's an 1863. The BBL has been glass bedded. That usually the sign of being a Skirmishers gun. Lots of guys in the N-SSA build guns, and glass bed the BBLs. Lots of those guys build very nice guns.
The hammer looks to be an original, along with the BBL bands, and butt plate, and nose cap. It could have original parts in the lock also. The lock plate is most likely a Repro of some kind. That might be an original BBl, that has been relined. How is the bore,??.
If you plan to shoot minnies in it you will have to find out the bore size. The best way to do that is with pin gages ( the negative pins). Then you want to size your minnies at 1-2 thousands under bore size. So if you size the bore at say .577, you want a minnie to be .575-.576. Use only pure soft lead. Wheel weights won't work. Also use good lube on the minnies.
Thats a nice musket. Good Find.
Dave