Wow, maybe I should go check my attic. Nice original addition to any collection.
The grenade launchers are quite rare, especially the carbine one.
I do think Underwood made barrels for Saginaw Grand Rapids Facility (Saginaw S'G'), and I will check my references later. This carbine was made near the end of production for Saginaw, so it is possible that they used some different manufacturer barrels to complete the contract. (last was 3,651,xxx) It is pretty unusual to find a rebarreled carbine. All US carbine ammunition was non-corrosive, unlike the M2 Ball ammunition for the Garand. Since the round was also lower powered than the Garand, the barrels simply did not wear out as fast, so they rarely needed replacement. This carbine has all the early features, and looks very original to me, even the stock matches. I would be surprised if the Inland is not the original barrel, need to check the barrel date to the manufacture date. Some good books out there, and you can google for much more specific information. Untouched original examples like this could be worth well over $1,800, especially if all the parts and barrel are correct. You really shoud get an expert to take a look at it. These carbines are quite a study, and to find a nice original like this one appears to be is truly good luck.
The 03 looks to have been arsenal refinished (FJA=Inspectors Initials(Colonel FJ Atwell), RA= Remington stock), as I think it would have a blued finish originally, and the barrel date is wrong. Probably manufactured around 1919. First time I have ever seen an 03 grenade launcher outside of a book, so I assume they are very rare. I would guess about $700 value or so.
Check out this website
http://home.att.net/~vishooter/m1903.html" onclick="window.open(this.href);return false; for lots of additional information.
Just a guess on the grenade launcheers, about 250 to 300 each, someone more knowledgeable here might be able to better help on this.
You must have some really good Karma to fall into a find like this.