the Lyman sights are original. Looks like the rear sight was bent to fit (sort of fit). On the BSA vintage forum, in the gallery section, there is one within a few hundred of yours with a two hole trigger block like yours. It has the push button cocking lever, unlike yours but is circa. 1920. Yours is probably late 1920/early 1921. Check out the network 54, BSA vintage forum. There is a lot of information and tons of photos to look at. And yes, your rifle has very nice bluing and superb etching for a rifle of it's age.