Photos sent to me by an email correspondent strongly suggest another possible--I would say probable--explanation for the crash. If Leeward's seat had failed during a high-G maneuver such that the backrest broke at the bottom where it meets the seat and fell backwards with him tightly strapped in, his hand being on the stick would have pulled it violently back causing the aircraft to pull up with tremendous force. He would now be in a prone position, unable to reach the joystick controls.
At that speed, the stress on the elevator assembly due to the violent stick pull-back would have been extreme, possibly breaking off the trim tab. There would probably be no way Leeward could sit back up and regain control. He may have been able to raise his head for a moment which one photo seems to show.
This scenario is supported by the fact that one of the photos shows the Ghost in her final dive with no-one visible in the cockpit. (See photo below.)
(There is another photo which seems to show a broken seat flying through air at impact.)