Interesting. Looks modern, and the steel barrels seem modern--Belgium was the world capital of laminated barrels (twist, "Damascus" etc) for a long time, and one might expect an inexpensive pre-WWII Belgian gun to have those instead of solid steel.
If you can post a real close-up of the proofmarks on the barrel bottoms and any others you see, somebody here may be able to get you more info like DOM and maker or at least the barrel maker. If you get no joy here, try posting on www.doublegunshop.com/BBS
(or if I got the URL wrong, do a search for doublegunshop and look for the BBS forum). Lots of really serious doublegun nerds there, and likely a Belgian one or so.
Neat little gun; thanks for posting!