Manufacture Leigeoise d'Armes a Feu--sounds much more prestigious than the English translation "Liege Firearms Factory"--but as noted above, they made some pretty nice guns, like yours. Too bad someone messed with the screws, but otherwise it looks pretty darned good.

If you're correct on the date of production, the appropriate proofmark would be 12 over a C (assume it's a 12 gauge) inside a diamond. If it's a somewhat later gun (post-1924), it would be marked 12-70 inside a sort of capital C. I'm thinking maybe a later gun, because it's a bit unusual to find earlier Belgies with 2 3/4" chambers (unless they've been lengthened).