The Graviner extinguisher was located on the outer (i.e. engine) side of each firewall, on the lower section. Pics I have seen, and actual installations, show this on the outboard side of the engine, and these were operated individually by pressing the (four) covered push-buttons on the...
American pilot on an exchange tour with the RAF in September 1970 or '71. Was on a night "TacEval" exercise, hunting a Shackleton acting as "enemy". Believed to have hit the sea, exited the sinking aircraft, and was never found.
Nice, although a tad pricey.
Bit dubious about the pilot figure though. As far as I'm aware, P-51 pilots used a back-pack parachute, with a dinghy/survival pack which they sat on. That also means that a seat back cushion would not be present. There may have been exceptions, but all wartime...