Walksfire,
I checked on your Spencer Carbine serial #47448. Hope you read my serial # disclaimer, if not, please read it
In my SRS books I find Spencer Carbine serial # 47450 issued to a member of Company D, First Vermont Volunteer Cavalry in February, 1865. OR, #47439 issued to a member of Company E, 19th New York Volunteer Cavalry in September, 1864. It appears that more Spencer Carbines in your serial # range (4700 (+) or (-) went to the New York Cavalry Unit.
Did you read my Spencer Serial # Disclaimer
Thanks for joining SSS
Two Flints