The Williams reciever sight is a very good piece, no projecting knobs to catch on twigs or branches. The existing open sight can be removed with the elevator, the elevator is a seperate piece that just slide on top of the barrel to lift the open sight up and down.
A "blank" can be gotten from who ever supplies the Williams sight, if not then Brownells gunsmith supply has everything. Don't forget to use "blue" loctite when installing the reciever sight. The red stuff is forever and will not come apart!