Here's a pic of the stock from my 6.604xxx WRA:
It is mentioned in Carbine Club newsletter #355 (Sept 2009) that WRA carbines in the 6 & 7 million ranges often have a number stamped in the same location. I have no idea what it means although someone here on the forum may be able to offer some insight.
HTH
P.S. I checked out the pix in your "Winchester 6,480,xxx correct bolt color?" thread and your stock looks much like mine, the main difference is yours has a circled P on the pistol grip heel where mine has a W