Thanks for the additional pictures.
Two more questions: Is there a punch mark on the underside of the barrel (6 o'clock) roughly centered between the front sight cuts? How many grooves are there in the barrel?
One suggestion. Loosen the three screws that clamp the scope tube and slide the scope tube forward. Leave about a 1/16" clearance between the front edge of the data plate and the back of the rear ring.
Your rifle was undoubtedly used and subsequently rebuilt at Rock Island Arsenal. The 9/43 barrel is in all likelihood the original as is the keystone scant stock with factory inspection stamps. I agree this rifle is most likely a DCM sales rifle.
i would not pay any mind to the assertions that there are "no records anywhere".