My first thought in looking at the last picture of your rifle was, "That's an A3 not a 03", with that flat tang, hole drilled through and the uncountoured cut-off boss. Then I remembered I have a 03 with a serial number dated to 11/42 (per Poyer's book) that has the flat tang, etc. but mine has the rear of the cut-off boss countoured but not the front. So it's evident that Remington was making A3 shortcuts on the 03's in the run-up to A3 production.