"W-B" -- A Winchester Stock on an IBM?

[F4Rio]

I have a 3.8 mil IBM with "W-B" stamped in the sling well and hand guard. I can't find "W-B" stamp mentioned in Ruth, Riesch or Larson and don't yet have a copy of Harrison. The "W-B" stamp is very clear and deep on both the sling well and hand guard and there's no very light L preceding them, as in "LW-B." The stock appears to be a Winchester -- flat fore stock bottom, a Late Winchester Butt Plate and three holes in the stock underneath the plate. The Crossed Cannon cattouche on the RH side of the stock appears to be in the correct position for a 1944 Winchester 2nd Block Low Wood stock as shown in Larson pp. 358 and 363. The pistol grip is unmarked. The M1 Carbine stock marking convention suggests Winchester supplied the stock to IBM for this 3.8 mil IBM. Was this documented anywhere?
Pictures:
Dropbox - photo 1.JPG
Dropbox - photo 3.JPG

Thanks for any help y'all can give.

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