If you use a Crookedbarn breech you can mount any sighting device that will fit on a 3/8in rail. Scopes, red dots, peeps, what ever you want. The Williams peep should be low enough to use on a 1377 without changing the front sight. Just be sure if you get one that it can mount on a 3/8in rail. Theres no reason you can't use a scope on a 1377, lots of guys do. The Crosman 457 mounts can be used also, but you're better off with a new (better) breech in the long run anyway.