Squeal Solved --- sort of embarrassing, $700 lesson in diagnosis....

[black_box]

So after going through hell and ripping out most of my hair, I found the issue that was causing all of the grief with my car (actually the 3rd issue on the clutch/IMS job). I was hitting my wit's end and took a diagnostic step that I should've done from the beginning.

I started listing on paper every conceivable way my car could be doing what I observed (loud squeaking from right-hand cylinder bank under engine load) with no regard to what I thought were known good parts, ranked them in order of difficulty to check, and then started down the list.

Even though I thought the noise was metal on metal or metal on plastic, I checked the spark plugs first. Turned out the #6 was a half turn shy of tight. How this happened I don't know, because I hadn't messed with them on this job.

I wish I'd done this first, instead of tearing out the transmission again and spending
$700 on a new flywheel and bearings!

Thanks to everyone who commented and gave suggestions as to how to find the problem. It's great having such a knowledgeable community of porschephiles to rely on for help.