Guy is correct. You have a postwar .38 Military & Police model that most likely shipped in November 1946. At that serial number, it should have either a 4" or 5" barrel. Post some photos if you can.
The gold K-22 Masterpiece box could be from as early as 1947, but they were in use well into the 1950s. Look on the bottom to see if a serial number is written there with a grease pencil. It could be black or white. That serial number will start with the letter K. The number will help us determine when, approximately, the box left the factory. As Guy noted, the box has value of its own, even though it isn't correct for your M&P.