My "Official Guide to Gun Marks, 3rd Edition" says that your proofmark of
E
LG
*
is the Belgian blackpowder proofmark, in use since 1810.
Belgium has a long history of producing arms. The most famous arms-making city is Liege, whose craftsmen began making swords, armor and related arms in the Middle Ages. Later, firearms began to be made there.
Liege is the site of the famous arms maker, Fabrique Nationale or FN. Making firearms for the world is still a major industry in Belgium.
The famous gun inventor John Browning went to Belgium about 1898 to have his first semi-auto pistol made, because American arms makers weren't interested in it. He relied upon the expertise and craftsmanship of Belgian gunmakers to make his gun.
Browning still has a presence in Belgium, though I'm not sure how much.
Why did Liege become such a major arms center? It sits on rich beds of coal and iron ore, and is next to a major waterway. Hard to get a better situation than that.
Anyway, Belgium exported millions of rifles, shotguns and handguns to America in the 19th century. Few were of high quality; most were average or shoddy. It appears that Liege flooded the hungry American market with guns as fast and as cheaply as they could be produced.
Today, it is not uncommon to find a shotgun or revolver, of questionable quality, shipped to America in the 1800s from Belgium. From what I've seen, there were more Belgian-made double-barreled shotguns than anything else.
Most of the rifles exported to America from Belgium were cheap, .22 rimfires and such. Seen a few of those.
I'd be mighty suspect of any imported, 19th century gun. It's probably a good thing that that shotgun is too far gone to be fired. I wouldn't trust it with black powder loads, let alone smokeless powder.
It's a wall-hanging decorator. Leave it as such.