You could try sandwiching the face in between two larger and thicker pieces of steel. Put the whole thing in a very large vise or something that would be able to squeeze and hold it straight. Heat the steel on both sides and compress. This would keep the very hot temp from the diecast. You may have to set up a jig though.
The broken corner if you have it Back up the metal with aluminum and drill and tap then JB weld it all. If it is too thick as the very corner, then just JB weld on front and back sanding smooth and blend.
Have had to improvise on these before.