They appear to be smooth rosewood (?) Target stocks without a cutout on the upper left panel, which would have been available from 1950 to about 1956. Do you see a stamped number on the insides? My guess is they were special ordered for a specific gun.
Only a few Target stocks were numbered to the gun, most of them mid-1950s Combat Magnums, 1955 .45 Targets and .44 Magnums. Please let us know what the letter says after you receive it?