As the gun has rebounding locks (ie post 1868) and you have the address info which seems to put it between 1870-1872 I think you have the date of manufacture nailed.Lack of choke also puts it pre-1875.My first impression on seeing the pics suggested an early 1870's gun. Congratulations on a very fine gun. I have a somewhat later hammer pigeon gun by Reilly that is a personal favourite.
Terry

Better to keep your mouth shut and be thought stupid,than open it and confirm.