Your Springfield .50-70 may shoot high as service rifles were designed to zero in with bayonet attached.
I think next time you are over or passing through you should stop by and borrow a few copies of Muzzleloader Magazine ..... every issue contains at least several articles and studies about early American personalities (generals, presidents, camp followers etc) and usually in depth articles about the frontier forts, politics and so forth. After reading what you wrote, I think you would really enjoy them!