New to me Remington M1903

[bigduke6]

Picked this up from an auction house on Friday, still needs a good clean but most of the grime has been removed, its definitely been in storage at some point as what looked like rusty areas were just grease and dust.

Magazine follower was caked in grease, this has had a plate spot welded in the housing to restrict capacity as it is a smoothbore so classed as a Shotgun in the UK.

Serial number dates it to 1942 it has a 142 dated barrel but a SA one, as SA were not producing the M1903, would NOS barrels from SA be used by Remington ?

The additional serial Number seen below the original I've seen somewhere before but cant remember where, also there is some stamp under the site base ?