Clayton,
Your Spencer serial # is 56319. Closest to your serial # is:
56331, a Spencer Carbine issued to Company E, 6th Indiana Volunteer Cavalry in July 1865;
also
56323, a Spencer Carbine issued to Company D, 6th Illinois Volunteer Cavalry in 1865 (no day or month listed).
Best info I have. Spencers were issued in no logical sequence of serial #s . . . please read my Spencer Serial # Disclaimer on SSS.
Two Flints