roboto,
Before you go off and buy the C&S rear sight read my recent posting on that subject. Their sight only works on -4 and later models without having to drill and tap the frame. If you find a viable alternative please inform us all as I have to -3's that would look better with the Extreme Duty.
http://smith-wessonforum.com/s-w-revolvers-1980-present/165055-i-want-combat-sight-my-old-66-a.html
If thats the case then I'm fresh out of luck.