Ron,
Need to see photos of your Spencer - nice sharp photos of the top of the receiver where the serial # is located. Also check under the forearm on the underside of the barrel for the same serial # - both serial #s should match. May have been one of many Spencer Carbines sent to Springfield for repairs and the Stabler cutoff was added.
With a Stabler cutoff, your Spencer may have been made near the end or after the Civil War. Photos would be a big help.
Two Flints