Summary: Today it turned over. No real explanation, but it worked.
I'd tried most of what was suggested in this thread, and had gotten to the point of going to Kragen and buying a spark plug specifically to check for spark w/o trying to remove one of the installed plugs. And then for a couple weeks I just didn't want to deal with it.
Today, worrying that if I let it sit much longer without even cranking the motor Bad Things would start to happen, I gave the -6 another try. For the second attempt I put the hand throttle all the way down -- and it stumbled after a couple revs. Hmmm... Tried it again, nothing. Started slowly raising the hand throttle, cranking, raising a little more, trying. On the third or fourth attempt, it caught and ran on it's own, anemicly, for a little bit. Hmmm...
Well, eventually I got it to fire and run. And in the process I filled the garage with the most godawful stench and grey smoke you'd ever want to behold!
I'm sure the neighbors love me, whooping and hollering while a foul-smelling cloud wafts out over their houses... By the by, the fluid trickling out of the tailpipe was greyish -- hard to say what if anything it smelled like,given what else was in the air at the time.
Anyway, the car smoked like a Navy destroyer laying down cover, but it didn't sound too bad so after spreading my smokey idea of joy through the neighborhood for a while I took to the highway to try and get everything warmed up properly. That tailshifter's still a pain in the ass, but the car felt pretty good otherwise and I think by the end the only smoke was the usual problem I have with condensate from the oil tank filter/breather widget dripping down onto the exhaust.
Just wanted to close out this particular episode, and again thank everybody for their help. Hopefully nobody's reported me to the DMV as a result of tonight's adventure.
Now, do I rebuild this lump or replace it with something that's got EFI...
--S.