On some notes I have scratched down here,
I was of the understanding that the Boxed WRA over GHD with the Crossed Cannons next to it was used on early Winchester I cut Hi-wood stocks. Starting from the first production to about serial 1,153,591. The Oval cut Hi-wood came into use at or about 1,067,649. So there would be a overlap where both I cuts were being used up while the Oval cuts were being introduced. Also the UN-boxed W.R.A. over G.H.D. with the CC to the side could be found on later I cuts, Oval cut Hi-wood stocks and the early type III Lo-woods. At about 5,5 mil or so normally you'd expect to just see the CC only.

Pictures are of a early I cut Winchester Hi-wood,



Note the cut recess at the top and bottom of the I cut in the oiler slot.
Now the oval oiler slot wouldn't have that type of recess cut in the top or bottom.
If your stamp is a real one, it's was most likely a type II Oval that has been cut down to a lo-wood and had the cut for the M2 added at that time or possibly later.
Look for any sign of it being cut down from a Hi-wood to a Lo-wood.
If there's no sign of it being cut down from a Hi-wood.....then someones bought a new stamp and been practicing.

hth

Charlie-painter777