Very nice pair !
The first version of the post war 6" K38 Masterpiece had a narrow rib barrel which basicly has the same frame style and barrel rib as the 4" Combat Masterpiece barrel.

Your K-38 was introduced in 1950 as the K-38 "Heavy" Masterpiece and supplemented the older version until around 1955 when the narrow rib 6" version was discontinued, The reason S&W went to the wider rib on the K-38 was so it would be closer in weight to the 6" K-22 and K-32 Masterpiece revolvers.
(they were heavier because of their smaller bore holes).

Both versions were standard in satin blue (like yours) with bright blue available on special order for a small up charge.
By late 1954 early 1955 the bright blue became standard.
Your target hammer could have shipped on the gun as it was an upgrade available also for a small upcharge with the standard style at the time being the "High Speed" or Fishhook hammer.

On a side note when the narrow rib 6" Masterpiece was discontinued around 1955 the "Heavy" moniker was dropped as it was no longer needed to distinguish between the two versions.
The "Non relieved" checkered K diamond target stocks appear around late 1949 and are a regular catalog item by 1950,
by around 1955 they appear with a small football shaped relief cut to aid in extraction as the non relieved style tended to get dinged by firmly ejected casings, even more so with the longer .357 casings in the K frame Combat Magnum introduced in late 1955.

On a side note although most post war target stocks were not serial numbered if you remove the right panel it could have a serial stamped there, if so and it matches your serial they were fit at the factory and originally shipped on the gun.

Your pre war gun is the predecessor to the K38 Masterpiece and was advertised as the .38 M&P target , These were basically the same as a .38 M&P revolver with the addition of an adjustable rear site and pinned patridge front site blade .
Notice your ejector rod is the earlier "Mushroom" style, this changed to a barrel style by 1931 IIRC with the separate rod end disappearing completely by around 1948.

If you post their serials we can narrow down the approximate ages but I agree the stocks on the M&P target are usually found in the early 1920's , if original to the gun they should have the serial pencil written inside the right panel.