IMO, your first paragraph says it all.

I have little confidence in "loaner" AMMs—especially the older ones with adjustable mixture trim pots. (what if the loaner is set way lean, and you may already be lean from air leaks? And it's 5°F ?)

Also, the experts say they've never found bad AMM with an ohmmeter. Which I tend to believe.

The only "straw" I can think of is pull and dry the plugs, then get the loaner AMM and check the trim pot resistance. Also check the trim on the one that had been running your car. Set the loaner trim to what yours was running at (or a bit higher?) and give it another try.

It sounds like you have several items that need attention, but I don't think any (or even ALL) of them would cause what you describe at the beginning of your post.
--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Sold 5/03)
'83 Turbo 245
'76 244 (lasted only 255,000 miles)
73 142 (98K)
'71 144 (track modified--crusher bound)
New 144 from '67 to '78
Used '62 122 from '63 to '67