the lettres annales indicates proofing in 1936 (O with a small flourish at 3 o-clock)....that puts it solidly in the era that daly imported o&u guns built by masquelier in liege....there is a quick way to spot these guns - their forearm irons have a peculiar angled shape inletted into the wood on the sides....have never seen that exact shape on any other makers guns.
i never owned one, but have looked at several examples over the years....12boreman has identified the models - and in my opinion they are not a "fine" gun, but well above the average belgian gun quality.
i see marking on the left side of the single trigger,...won't be surprised to find it's a miller....looks like a nice gun - maybe with a touch of choke openings.
https://littlegun.be/arme%20belge/artisans%20identifies%20ma/a%20masquelier%20gb.htmbest regards,
tom