I never had any of Harrison's books on firearms due to the amount of incorrect data. I would disagree with his stamped WRA trigger guard story until some supporting documentation was to surface that would prove without a doubt that Winchester manufactured a stamped trigger guard.
Even Scott Duff's book on the WW2 Garandicon states that Winchester used the forged type trigger guard until the end of production.

I have seen alot of data sheets on Winchester rifles including the Win 13's but never a stamped trigger guard.