Tom:
During 6 years of extensive field-based exploration for physical evidence of sites and trails used by Cole's Eastern Division in NE, SD, WY & MT, I have discovered both 56-56 and 56-50 Spencer shells, cases, and bullets. Therefore, I've concluded that many of the Eastern Division troops were equipped with carbines that fired such Spencer ammunition. I now believe most of their carbines were a mixture of the original and 1865 model Spencers. However, per Gil's comment, they still may have had some other types of carbines that were modified to use Spencer ammunition?
Sherry