I forgot to mention that this does have the bayonet lug. What does this indicate
That like most M1 Carbines, it was updated after initial manufacture.
Does it also have a twist safety? Early guns had pushbutton safeties that were too often mistaken for the mag release, so the safety was modified and retrofitted.
Early guns had a simple, L-shaped sight that gave you high and low elevation adjustment, but a fully-adjustable rear sight was later designed, and again, retrofitted to guns already in service.
Then you have high wood, low wood, potbelly stocks, M2 stocks, round bolts, flat bolts, etc., etc. It's great sport to try to figure out which parts are original to a given gun, or at least are "correct" in configuration, even if not original.
Other than the barrel, I don't know that my Carbine has a single original part on it.