More welcome "by the way" gems for us to pick at, Danny, thank you!
Your rear crew-man must have had some official status, presumably that of Air Gunner, as you seem to characterise his navigational skill as simply the ability to find the aircraft in order to climb into it! I think if I had been in his shoes I would have ever happily traded sight of the altimeter for the opportunity to sit facing rearwards and hence fully supported by my seat back, in preference to hanging by my straps in that prolonged vertical dive towards enemy ground fire. What the eye don't see the heart doesn't grieve over...on the other hand collecting a lap full of machine guns and ammo on the way would be rather a turn-off!
The most scary part of your post though is the ability of the elevator trim to arbitrarily wind in nose down trim into a dive that will already require all your strength to pull out of anyway! You saying that no one really knew why, and that the DS solution was merely to keep an eye out for it, hardly inspires confidence. I wonder if the pampered pilots of the MkIV had to contend with the same phenomena? Probably not, as it seems that they, like me, simply passed their time in straight and level flight, though whether tea came on the hour every hour I rather doubt.
Keep it coming Danny. It's pure gold!