A coda to my last post:
I got a few quarts of Brad Penn Classic GL-4 80w/90 from Summit a week or so ago, and dumped the $17/qt Redline oil to try this. I think this is better. The syncros are still tight, but loosening up. I'm at about 200 mi on the new transaxle (the weather has been horrible. Mother's Day was colder than Christmas 2019), and I'm only having occasional issues downshifting. I double clutch most times to get into first, but even that is loosening.
This is giving me practice rev-matching every downshift (it's a bit different with the 2110-- it doesn't spool up quite as quickly as the twin-spark motor).