I can't comment on that model rifle, but the tang sight is a peep sight of course.
Usually, you will be able to shoot tighter groups with a peep
rear sight, as compared to open sights.
I have used three Marlin Guide Guns in .45-70.( Much shorter barrels )
Two of them shoot very well, and the third one I have not had
time to check out fully yet. I suspect the rifle will do very well with
loads that it likes though.