Kevin,
(From the Shiloh ad) "This is the model 1860 which is the correct model for Civil War use. It has all matching serial numbers of 51,998, which is within the Civil War production since they started at 11,000 and went to 61,000 before the war ended."
Closest serial # to the above 51998 is a Spencer Carbine, serial #51991 and #52002 both issued (among others close, too) to Company B, 14th Kansas Volunteer Cavalry on March 25, 1865.
Price may be a bit high for a late Civil War issued Spencer Carbine, in my opinion. Condition is everything in determining selling price.
Two Flints