I Have my Robar NP3 4506 back! After 10 years apart we have been reunited and are in counseling.
XS Sights is working on a solution for me as i really want the Big Dot sights, i have these on two of my Glocks and they really help my old eyes and my shooting scores went up drastically.
The 4506 adjustable sights i have according to S&W and the forums here use a rear sight from their K/L/N models. XS sells a rear adjustable sight for the 686 that might just work. The trick is will it line up with the big dot front sight purchased seperately that they sell for the 4506. i will keep you guys posted when i hear back from them, they are all at the shot show. otherwise if that doesn't work i will have to go with the Trijicon SA-02
Semper Fi