They are made to fit current round-butt S&W K and L frames, as all square butt frames have been discontinued on regular production revolvers. They convert the round-butt to a square-butt configuration. Altamont, who make a lot of special limited-run stocks for a number of manufacturers might, or might not, offer them for the older square-butt L frames.
Back when... Smith & Wesson was still making square-butt K and L frame revolvers they also made "target stocks" somewhat similar to the ones you are looking at. Shop around Ebay and other Internet auctions and you might find a pair.