Plugged holes in my no2 mk4 .22 Trainer

[Old Lancer]

My No 2 Mk4 has these plugged holes in both sides of the receiver behind the charger bridge, the job has been well done and appears to have been done many moons ago, anyone care to hazard a guess what they were for?, and if as I suspect they were to mount an aperture sight can anyone tell me which one?
Like most other trainer owners this is one of my favourite rifles, it can out shoot plenty of modern .22's if it's owner is brave enough to dismount the scope.

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[Old Lancer]

Upon further examination i have also spotted four plugged holes in the charger bridge, three on the left and one on the right, also the rear of the charger bridge has been milled out to form a full width 90 degree channel, any ideas?

[fergs]

the ones on the charger bridge looking at some of the pics of mine should be there as the charger bridge is soldered and pinned on the action this would explain the plugged holes either side of your charger bridge. As for the other two plugged wholes is any ones guess!.
Regards
Fergs