Ok, that's a legit number, built somewhere between December and end of January '44
http://www.vishooter.net/ra_serialization.txt
The single box is still an issue. Everything I've found says 1903A3 were crated ten at a time, 5 butts to the left, 5 to the right. So, a true original crate would be a large thing, with 9 empty spaces.
DCM is possible, I do not know how those were shipped. The successor to DCM, CMP buts rifles in a hard-side case which goes in a very plain cardboard box.
I suppose we cannot discount that someone inside the Remington plant might have sticky-fingered an A3 into a plain "company" box. But how that was not caught in the serial number audits by BuOrd or Ordinance Corps.
Almost too many questions.
Now, were this without the box and its questions, cleaned of cosmoline, it's worth about $1200. Since it should be a '44 build, it should have all stamped fittings--trigger guard, barrel bands, etc. If it has milled parts aboard, then this was rebuilt by major unit armorers, or it was rebuilt in 1950 for Korea, and then cosomlined. In which case, the value takes a hit, down to about $800, assuming all the cosmoline is cleaned up and the stock is pretty. Now, if the barrel date is not 1944, or some of the parts are not stamped "R" the value will tumble a bit more, call it $700.
If we can solve the riddle, we'd be closer to what the antique museum people refer to as "provenance." That's because a good story adds value to things. See, if some remf from Mark Clark's G-3 shop sticky-fingered this thing and got it rotated back to conus and it's been in an attic since 1953, that would be a provenance, and be worth a dime or two (about 5000 dimes or more)