That can be welded up,both sides,then they can be shaped and dressed up with files and sandpaper.I have redone cases with 3 finger sized hole and no case chunks to weld in.
A good welder can build up,and or reattach chunks,rather easily.Inspect the top case in the chain area,clean it good and use a good light to see if there are any small cracks there which could be addressed by the welder at the same time. I put a chain threw a set of cases
(top & bottom),fixed it and that motor is still running fine today.That was in the summer of 1975. Head