Yes, but how is the gas shackle element of the modification programme related to the weight problem? This appears to be more about improving the release of the drogue chute from the seat, and deploying the main chute.
It is true, as Easy Street states, that the "offending" bolt and shackle remain and can be "wiggled", but they are no longer the point of release as they are with the scissor shackle. From the drawngs associated with SIL704 it seems that a lug is permanently attached to the drogue shackle by the bolt and the other end is attached to the gas piston assembly. This becomes the point of release.
On the face of it, it would appear that if Flt. Lt. Cunninghan's seat had been fiitted with a gas shackle, rather than a scissor shackle, he would have survived. Perhaps the SI team and the Coroner were encouraged to wear "Hawk" blinkers rather than the Mk10 modification programme as a whole.
DV