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.)
The tail wheel extension might be due to Leeward grabbing at anything in the cockpit in an attempt to pull himself back up. The landing gear lever in the P-51 is fairly large, looks like an emergency brake lever and is just to the left of the seat. That might have been the only thing he could grab from a reclining position. As I understand the WW II Army flight manual for the P-51, the gear lever is supposed to lower both the main landing gear and the tailwheel, but aerodynamic forces at that speed may not have allowed the main gear doors to open.
FoxNews did a pretty good piece on this, with Jim Nance, who, as a former airline pilot, is about the only qualified aviation spokesman in the media, quoting a certified P-51 mechanic who suggested that seat failure could explain the absence of the pilot's head in the canopy. (It is typical in many older fighters to have space behind the seat for storage of personal gear for cross-country flights.) Based on the photos and a little more research, I am strongly inclined to believe that this is the most likely explanation for what happened. I feel for Jimmy Leeward and the horror and helplessness he must have felt at what was happening.