There are, or were, a number of outfits that made an adjustable iris aperture. Use smaller opening for target shooting and bright light conditions, use larger opening for lower light conditions, hunting etc.
I do have a spirit level on a Browning High Wall. Must say I'm not impressed. I find it to be more of a distraction than a benefit, but that's just me. Others may like them. I tend to think of the spirit level as an aid for someone who does not have proper form. Again, just my view.
I think you are going to really enjoy the sharps. They are too big, heavy, awkward, did I mention heavy. But I've got to admit, I do like to shoot them. I've carried mine 15 miles through the mountains, during season and plan to do it again. There is just something about the Sharps, I never feel under gunned