Uncle Miltie
50 Cal.
Correct, but I don't think the Soule was available to shooters until 1892. Pedersoli makes a sight similar to the old Goodwin sight, but much heavier.Soule type sights are used happily and successfully by many on military target rifles such as the Whitworth and Volunteer models. If period correct / spirit of the original is a factor, keep in mind that they post-date the rifles by 25 years. J.W. Soule patented his sight in the US in 1889 - so well into the breech loading era and unlikely ever to have been used on a British rifle from the 1860s.
David