Looking at a hi-res image on Winchester's web site of one of their 73, that appears to be a common Marble's barrel mounted sight. Brownell's sells a number of variations, all with a bead. There are two widths, 1/16 and 3/32 as well as a few bead colors and sight heights. These are one piece, so just remove the sight, clamp it in a vise, and file the front face flat to either vertical or slightly sloping away. Blacken the filed face with flat black paint and re-install. You can do the same to the over-hang towards the muzzle, too.