well you have an Underwood M1carbine that has mixmaster parts, most do due to the rebuild they went through after the war. Serial number puts manufacture date range of July 1943-March 1944 but closer to early 1944 I would imagine. Barrel date of 11-42 indicates barrel was probably replaced at one time. It s always possible that the 11-42 barrel sat in a bin at the bottom and was pulled out for your later 1943-early 1944 build. It is possible that someone changed the barrel recently as they as well, quite a few try to re barrel a BLUE SKY import marked carbine to increase value and perhaps put the old barrel on the other one they swapped it from. As it is import marked BLUE SKY it is the least desirable of the imports due to it's large printing and sometimes heavy stamping that caused damage to a few barrels but we will never know when this barrel was placed on the receiver, we can just speculate. Inland slide, Inland bolt, Inland hammer. We would need more pictures of other parts for ID. $730 with 4 mags is not too bad, probably high on the BLUE SKY import totem pole but still ok if it shoots well, that, after all, is why you bought it.
http://m1family.com/topic14.html
U.S. Carbine Imports & Exports