First- go get this tattoed somewhere you can see it easily-
"Buy the gun, not the story."
Now, IF it is a Winchester, and it is in shooting order, it is almost certainly worth $130. Just for grins, if you offered a $100 bill and a $20 bill, you would probably own a shotgun. If it IS a Model 12, worth well over that. You can get a replacement stock for a Model 12 at Numrich (gunpartscorp.com)
Not all military shotguns were Trench Guns. There are riot guns, guns used to guard prisoners, used to train aerial gunners (learning to lead clay pigeons), and guns that belonged to the recreation sections. A true military shotgun will usually be marked with the flaming bomb mark of US Ordnance, and US PROPERTY stamped on it.
The doo-dad by the trigger may be the release for the slide- allows you to pump the action without pulling trigger. Used to load/unload chamber.