Hello
The "S" prefix before the serial number tells yours was made between 1964-1969 Era. They started the N Prefix after 1969 that so it leaves your in a short window for collectors being only a Five Year span using the S prefix. Nice Looking revolver, and if those grips are original to it they should be stamped on the right Panel with the guns serial number and seeing the diamond missing they came after 1968 time frame as that is when S&W stopped making the diamond center grips. One odd is, I noticed is that they are not the P.C. style grips. Most model 58's came with the scalloped edge P.C. Style grips back then and Perhaps they are not original ? If the right panel has the guns serial number, it had to have been ordered with those style grips, and I would be willing to bet it was one of the last to get the S Prefix before they changed over to the N Prefix in 1969. I hope this Helps, Hammerdown