I repaired one that was almost identical, myself.  One hole had already been drilled by someone, right in the P proof mark, and a screw put in.  So I just drilled a couple more holes, countersinking them so that I could later put wooden plugs over the heads of the brass screws.  Next I mixed up some thin clear epoxy and used a syringe to inject the epoxy through the holes until it flowed out the crack.  Then I tightened the screws, cleaned the excess epoxy off and put my wood plugs over the screwholes.  It ought to be good for another 100yrs.  That's what I'd do if I were you.  Take your time and you'll hardly be able to tell it was repaired.  Yours is a bit longer than mine, you might need screws from the bottom near the front and from the top near the rear.