Just got home from up North, pulled the corrugated shotgun butt plate off and the stock doesn't appear to be hollowed out aside from the main screw hole. The hole is .79" or 20mm wide at the opening. Is the hollowing at the tang side? All serial numbers match BTW.
-Connor
If your numbers match your rifle is right. Yours was probably one of the first to not have it butt stock hollowed, if you see Calhoun's notes above.