I have installed an aftermarket Millet rear sight on a M66 at one time. It required no smithing and if I remember correctly, it could be had in different sight configurations, ie; plain, white outline, or tritium inserts. Mine had the tritium inserts.
Cylinder & Slide Extreme Duty Sights are what you want. Often they work just fine with the factory front sight. I have a set on one of my guns and love 'em!
The catch is that the mounting holes are spaced for post-93 guns that are drilled and tapped at the factory for scope mounts. Pre-93 guns will have to have the top strap drilled and tapped for the mounting screws.