BR,
Good point on the no raised metal around the "US Springfield Amory and serial number.

"One thing that impresses me about SA 'markings' is that they don't seem to disrupt or displace the surrounding metal. Oddly, sometimes a SA marking will be inconsistent in its depth. Clarity of letters and numbers is variable. Fake marks are often noticeable because they disrupt surrounding metal and finish."

The only way to have done that is to buff them before heat treat.
The proof "P" on the front to of the receiver, does it have raised metal around it? If so it and any other marks like it would have been done after heat treatment.

I just want Mark's carbine to be a one of the kind original worth a million bucks. Then we could all wish we had one also.