Hello bill, are you a member of the Austin Gun Club? There are several forum members that belong and are members here!
The grips are replacement by the GI or later.
The 1938 is the year made and the S/42 is the manufactuer (Mauser).
More precise info, what the proofs and acceptance look like on the right, full serial number to include suffix (the letter on the front of the frame just below the serial number).
Ed