You could easily weld the lumps on. But you would need to put large "V" weld prep under the area where the barrels attach. Then normalize the area before machining. This sort of work is done a lot in industrial applications where force and pressure exceed the amount proposed by a firearm. But it is also not an easy weld to do and if you are not trained it will crack or have inclusions and porosity.

And the gunsmiths I know are not welders. It is not something they are comfortable with or do with any regularity.