Hi John, …
Well, you had me until that last sentence.
No, this rifle has all the ear-marks of a professional build or assembly. Both the metal and stock are in VG-to-excellent condition.
And given the provenance from my gunsmith friend from whom I bought it, as was described in my O.P., his father acquired it decades ago from the DCM, not recently. It wasn’t something his father or anyone else “Bubba-ed together” in a dark corner of a basement.
Your earlier statement that, “The replacement was most likely made by a company armorer during the latter part of WWII,“ meaning a Remington armorer, is most likely correct as to how this 1903 came into being.
How it eventually got to the DCM is a different question.