The bayonet lug and adjustable rear sight means it is either a very late one, or arsenal reworked.
Original ones did not have the bayonet provision and had a flip over L rear sight.
Not that this is bad.
But again, I would post, with pictures, over on CMP Forum M1 Carbine section.
They will give you a good idea of what it is worth.
I was happy, they came back in the $1K plus range, for the one I picked up for $800, with accessories, so mags, ammo, and spare parts.
Thanks. I plan to do so. As mentioned, I'm less concerned about its worth than I am about any historical value. If I can ensure that it's been arsenal-reworked in the postwar era, then I'm less concerned about keeping it intact (those gunsmiths "broke the seal") and I'm willing to lightly mod it for my purposes (scout-type rail, and perhaps a stock if I see something I like).