SSSETOWTF,
Nice post - clearer and more comprehensive than mine. The picture looks like a fairly old version of the IPP installation.
I was closely involved with the early studies into the installation that resulted in the redirection of the exhaust from up to down on the B. I believe the A went that way as well. However, a lot of people on both sides of the pond got really excited over the issue and the C stayed with an upward exhaust. For the B it was a good move - saved a lot of weight and resolved quite a few issues with the routing of that vertical exhaust.
Best Regards As Ever
Engines