Recently a couple of product code 103958 have sold on Gun Broker, Standard Catalog of Smith and Wesson 3rd Ed. lists it as "Reported as Classic Hunter, fluted cyl., 6.5", rubber grips, not verified.". The one auction did have a photo of the box label showing the product code 103958, so maybe we can call this one verified now.
If anyone has any other 657 product codes that I haven't pictured please by all means feel free to post them here.
KO