I have repaired worse, but cannot speak for how well they stood up to use.  Even given careful repair, and equally careful filling of voids with same species of wood-dust mixed into epoxy, one will always be able to tell that the wood has been repaired, although often this requires a close look.

Trick is the apply the epoxy in a thin, uniform layer throughout the entire crack, and then to clamp the repair as tightly as possible without marring the surface of the wood.  Also ensure that the edges of glued joint are accessible, so that excess epoxy can exit the joint (and be wiped away) as pressure is gradually increased by clamp.  Don't clamp tight initially; wait a few minutes with light pressure to allow excess epoxy to be squeezed out, then add some pressure, remove excess epoxy, and repeat.

There is a lot of surface area there available for gluing.  Assuming the wood in that joint is not oil-soaked, the Epoxy repair should be pretty strong.  Add epoxy to voids after initial gluing, and sand down to flush.  You'll need to re-finish the stock to "hide" the sanding, and make things look as pretty as possible, but don't over-do it; this is a military stock, and it's not supposed to have a top-grade finish.

I second the idea of a beater syn stock for everyday usage.