You are now a member of SSS. Please take the time and post photos of your Spencer, especially of both sides and top of the receiver area, with the breechblock extended or opened up.
I checked on your serial # and I'm sorry
to report that your serial # doesn't allow me to make even a guess as to what Civil War unit your Spencer was assigned to. The serial # for Spencers are very incomplete and they jump from one number to another without any kind of order. I would only be guessing about yours . . .if you post photos with your original post maybe someone will offer you a better idea of the Civil War unit your Spencer was issued to . . . Company L of the Second New York Volunteer Cavalry is the best suggestion I can make, issued to a member of that unit in March of 1865
Send your photos to me at email@example.com
and I will post them for you. 5 or six clear, sharp photos would be OK.