S&W adjustable sights are primarily a matter of getting two things correct.
First is the length. The newer vintage sights are about 2.6" in overall length and have the rounded front tang. While they will work on older vintage Smiths, they look awful, because they don't completely fill the rear sight cut out on the old guns. The vintage adjustable rears were 2.75" in overall length and, as mentioned, were square in front. If you want one of these, you need to go shopping for used sights, since no longer sold new.
Second is the rear blade height. This is trickier, because blade height is a function of not just the cartridge, but the barrel length. A model with various barrel lengths, then, might have used a couple of different rear blade heights.
As for the lock, I've owned a couple of dozen Smiths with the lock, including the big nasty 460 and have never had one fail. You can remove it if really bothers you. Do I like it? No. Just a useless feature for me and most users. As Mistered says, though, the absence of a lock is a convenient way to separate the new stuff from the vintage. The vintage Smiths are valued for a lot of reasons other than the absence of a lock, but the lock makes them easier to spot.
