From what I can gather on the net a S&W distributor had some pre-Model 36 Chief's Special revolvers made up with adjustable sights, those had 2" barrels and were made starting in 1955. There may have been other variations but I can't find a lot of info on those. The Model 36-6 with the 3" full underlug barrel and adjustable sights was a limited run of 615 pieces made in 1989.

[Linked Image from morphyauctions.com]

S&W made a bunch of Model 36's in a 3" fixed sight configuration and those are fairly common.

[Linked Image from hyattgunstore.com]

Gunnery, gunnery, gunnery.
Hit the target, all else is twaddle!