Rim Fire,
The Spencers issued to the 8th Indiana Cav are TOO scattered over TOO many serial #s to list accurately. Interestingly, I do find a Spencer serial #7728, BUT this is a Spencer Carbine issued to Company E, 11th Ohio Volunteer Cavalry on 08/21/1863.
Not sure what else to tell you . . . ask me more questions. Or send me a PM, or Email.
Two Flints