Welcome to the forum. S&W did not use model numbers until 1958 and your gun was made before then. It is a K38 Masterpiece, which when they began using model numbers became the model 14. Looks like someone drilled it for a lanyard ring at some point and obscured the official serial number which is a no no.
Well, in the US it would still be a problem, as the cylinder serial number (and the one on the barrel, etc) have NO legal meaning to identify the weapon. For the purposes of United States law, the receiver or frame is legally the firearm, and as such it is the controlled part. The definition of which assembly is the legal receiver varies from firearm to firearm, under US law.
Barrels and cylinders are expected to possibly be replaced during a weapon's life... that is why their serial is irrelevant legally.
As an example, with an AR-type weapon, the lower is serialed - you buy uppers without serials, and one lower can have several uppers in different calibres used with it without any legal issue.
With the FN-FAL, in contrast, it is the upper assembly that is serialized and legally considered the receiver.