Any pistol grip not marked with an ordnance belted cannons can be considered a replacement grip. The upper wood of the stock was never marked with manufacturers marks or the ordnance mark on the right side like M1 stocks. These are not only fakes but bad fakes. Winchester never made M1A1's and the markings are in the wrong place. Original M1A1 stocks did not have a selector switch cut out for M2 usage.
Many reproductions do.
The finish should be parkerized. The butt plate is a single cast item with the markings B257614 followed by a sunburst type marking in a circle and a drawing number from 1-12. It is important to look for these markings on the inside of the butt plate. All genuine stocks will have these markings. As well be certain that the numbers are CAST into the butt plate and not stamped.