Multiple folks who know more than me have told me that the RRA stamped stock is actually a late Winchester, not IBM, though several also have told me that it is common for IBMs in theat serial number range to have "IO" stamped flat bolts, so that may be original to the gun, meaning stock and rear sight are the two items replace at Red River arsenal.
Also that the 1963 NRA sold carbines often had upgraded rear sights , but retained the type 1 barrel band. My first carbine in 1982 was an 1963 NRA gun, and it was a Winchester with late sight and Type 1 barrel band.