This 57 looks odd. I have a 57 that I acquired in '92 which had what I believe to have been a 3 screw side plate. I believe that mine doesn't have a side plate screw just below the rear sight. From the looks of this picture, it looks like this Smith has a 4 screw side plate reminiscent of the old 5 screw Smiths.
In doing some research tonight, the Smith in the above photo is a Model 57 Classic, which apparently is carrying the fourth side plate screw. I wasn't aware of the Classic 57, shame on me.