I'm in the "hard to tell but definitely questionable" category when it comes to SLE vs BLE. I've seen plenty of sideplated Belgian boxlocks, but most of them don't go to all the trouble with the fake pins etc to give the appearance of a sidelock.

The guns do have 30" barrels. And at least on this side of the pond, 1 1/8 oz loads were available for short-chambered 16's. I've also seen and shot a Bernardelli 20ga hammergun set up for live birds, so while anything but a 12 is certainly less common for pigeons, not impossible.