While not a a militray no4 stock (I assume) Im left wondering.

[Mk VII]

It was a piece of eyewash, and most people used the P-H equivalent with just a short screw through the left pivot and didn't seem to notice any defect.
My club has got several of these Excels, which they want to dispose of. Hardly anyone does centrefire rifle now, and those who do own their own gun.
The inletting will be for a handstop rail. I had an Anschutz rail put in my Mauser conversion.