The center rifle is obviously a rebuild as witnessed by the slide on the rear sight which is a contract item not an SA product. Later contract stocks were inletted for both the 03 and the 03A3. According to both Brophy and Campbell, all 03A3 stocks were inletted for the FRSB. I know that Keystone stocks were a contract item that was inletted for both 03 and 03A3 as I mentioned previously. I cannot read the S/N of the center rifle but the lettering looks fairly early , maybe even SHT, a number of which were rebuilt, issued used during WWII. Note the difference between the elevation slides on the left hand rifle and the center rifle. .
FWIW