Only the very early S&W Model 60 and a few early Model 66's actually had real stainless steel hammers and triggers.
Early on, S&W determined that they didn't like the way the stainless steel parts wore, so they quickly changed to standard case hardened carbon steel parts, to which they applied a flash coat of hard chrome to match the actual stainless frame and cylinder.
Later in the 1990's, as a cost savings, S&W stopped applying the hard chrome.
In any case, NEVER stone or alter S&W hammers or triggers. The case hardened coating is extremely thin, and virtually ANY amount of stoning will break through the coating, exposing the soft inner metal, and ruining the part.
A sure and certain sign that an incompetent "gunsmith" has been inside a S&W are stoned hammers and triggers.
The factory and most real gunsmiths will automatically replace any S&W hammers or triggers that show signs of stoning since it's almost certain the parts are not safe and are ruined.
So, the parts for sale are almost certainly NOT stainless steel, they're standard plated parts as used on all S&W stainless guns up until the 90's, and under no circumstances should you stone a revolver hammer or trigger, S&W or any other brand.
It's very common for people on the net to claim that guns or parts are stainless steel, when they're in fact, hard chrome plated.
When asked if the parts aren't really plated, they invariably swear they're stainless, since to them, they LOOK stainless.