Any carbine authentic for the Korean or Vietnam War will be a mixmaster; especially since the fat M2 stock as replacement for the original skinny M1 stock, the three nub banana magazine catch for the two nub stick style, the adjustable rear sight for the "L" flip sight, the flip safety for the push button, the barrel band with bayonent lug for the earlier narrow and broad plain bands, were preferred replacement parts during arsenal rebuilt stateside or over seas after WWII. Objecting to a U.S. M1 carbine re-imported by from Blue Sky Virginia from Korea as a "mixmaster" is ... odd. An all-factory original would not be authentic for the Korean or VietNam era.
A lot of the original WWII contracted manufacturers subcontracted parts to the original Auto Ordnance, Marlin Firearms, and other factories anyway. A lot of U.S. Carbines left the factory with parts from mixed makers.