If you do by a reproduction rear sight, look for the one on the left in Blair's picture. The same picture is on page 82 in Marcot's book, and it states "the left (sight) is the rear sight found on all model 1860 Spencer carbines and rifles. On the right is the rear sight that was put on the model 1865, and model 1867, and New Model carbines and rifles. I would hate to see you put the wrong sight on your 1860 rifle that appears to be in the Wilder brigade range. Original M1860 sights go for between $135-160. A good reproduction M1860 sight is made by Rich Cross. They are sold through S&S and go for $85. Best of luck.