Well here is an update, so this thread is complete with the question
AND the answer.

Last night I pulled the engine again, found that the flywheel was in
fact loose. I tightened it with this cool 9X torque converter I got
from aircooled.net, put everything back, and to my satisfaction and
joy, the noise was gone. John Muir's "engine sounds" were right on.
It can be kind of hard to hear it on a recording, and an old recording
at that, but the sound was dead on and it helped me realize the problem
that I wouldn't have guessed otherwise. Everything looked ok as far as
the dowels and all that. It must not have been too loose and I didn't
drive it much at all so I was lucky. Hoorah! Did a 5 mile road test
and filled up the tank while I was at it. Everything in order at last.

Note to other ameteurs: This torque business is serious business. My
torque wrench only goes to 100lbs so when I originally did it I just
did it as tight as I "dared". That was clearly not enough. With the
9x converter I could pretty easily find 30lbs on my wrench (which would
be 270). I gave it about 35 just to be sure (have to be careful not to
go over though with a 9x muliplier).

Let me again express my appreciation to the existence of a message
group like this and the kind people on it for being out there and being
willing to offer suggestions. This kind of resource was not possible
10 years ago and it's just completely awesome.

Thanks,

Chronlogic
--Now with a bug of my own doing on the road and thrilled about it.