I would think that from the video ,at Pylon 7,that GG hit wake vortex from Strega and Voodoo,who were approximately 4-5 secs ahead,GG having overtaken `R-Bear at this point.That may have triggered the failure of the left tab,the Mustang has two trim tabs,but there does appear to be a difference in deflection,looking at the `oil-canning` pic.#207 ,and the other left -side shot.#162.
The EAA article mentioned earlier,Jimmy says the ac stalls about 130 mph,but cleanly. I would estimate the wing area at about 175 sq.ft,and at about 8000lbs a wing loading about 46-50 lbs/sq.ft.,so I would guess a peak `g` of about 15.. but what is telemetered depends also on the position relative to the Co G.
Whilst it has been poo-pooed ,the seat may have failed,depending on its mountings; it also looks from the other slideshow link,that the harness mounting is somewhere behind the seat and below the pilot` shoulders,ideally should be above/level,and attached to the main a/c structure...certainly used to be for F1 air-racing,when I were a lot younger..Similarly, it could be that ,being forced down and forward,JL could have been struck by the control column,in the chest/face/neck.
Just another point about the `oil-canning`,in that particular area is where the structure normally houses/supports the radiators; however I would be surprised if the area had not been strengthened to accomodate their removal.
I would suspect that next year there may be aircraft with `trimmable stabilisers`back in vogue.
As an aside ,I think Matt Jackson should keep it zipped until the investigation is over..