I picked up a relic (dug) Spencer carbine on Friday from a local guy. He said he knows who dug it so I will have to see if I can get more information. SN on the receiver is tough to read but you can make out a 543. SN on the barrel where it was protected by the wood for however long is very clear 54373.
According to Two Flints it is a direct hit in the SRS for company M 1st Alabama Cavalry issued on 6 Nov 1864.
I may try to clear up some of the receiver if I can.
(Photos re-posted by Two Flints)