If it is a single break-open, I was not into the single shot shotguns much.
Not going to bring much, first you have to find someone who wants it...
A good spot to find out the value is a gun selling location and they are going to give you a value based on condition.
So with that in mind there is the place to start. With that long barrel it was a specialty shooter for long range, more then likly ducks/geese.
It can be used but not for much, I would say. Does it mention the choke? Full ?
Having it on a wall is ok, problem there, is it will be stolen. Sad but true.
Relegated to a safe or sell.
When you say you found it are you looking to buy?
If that is the case you want to buy as low as they will go if selling try to get as much as you can.
Good luck,
HQ