Happy Hunter - thanks for your reply on the Model 10, the info is much appreciated.
Concerning the M48, there are no number/letters before the K, and no letters after the K. I double check the serial, and it is what I had posted.
Although the Model 10 we knew was fairly recent, the model 48 is much older. Unfortunately, the person who originally owned it passed away, but has been collect S&Ws for 50 years. It could date a few years back.
Does anybody know of an on-line resource to help date S&W's