The flywheel is tapered on the back so it comes nowhere close to touching the front seal. My idle gap looks to be about 0.75mm -- a little wider than Geezatec's, but the lowest I can adjust it without the engine stalling every time it drops to idle.

I ran the car again today, and it behaved fine. I loosened the LSN a teensy bit, and I tightened the HSN fairly substantially because for some reason it was running rich enough to bog-down when I revved it. I haven't run it since spring, so it's entirely possible the weather has changed enough that a re-tune was necessary anyway.

The interesting part is, even though I had to lean-out the HSN quite a bit (over a full turn), it never exhibited the fluctuating idle that I'd had trouble with before. It could be loosening the LSN a teensy bit did the trick, but I don't think that's the whole story, because I had to fight with the engine to get it up above 200°F -- something I've never had to do before. Usually that engine is hard to keep below 240°F.

Aside from the cooler weather, there is one other change since spring that has been proving to be significant for all of my vehicles -- I spiked my 30% nitro with an extra 1% pure castor oil. All of my engines are running better because of it -- I can push them harder and they stay cooler, presumably because of the better lubrication, and perhaps slightly better sealing caused by the slightest hint of varnish on the parts. (my Byrons Gen2 fuel uses a synthetic/castor mix, but it's degummed castor so it doesn't leave varnish behind -- I'm starting to think that's actually a bug instead of a feature.)

So in short, it seems to be working better and I have no idea why -- only guesses, and tenuous guesses at that.