After mentioning this to the epic Classic Saab Facebook page, I got a number of suggestions. One was to, of course, check compression. Another was to attempt a start manually manipulating the air plate.
I tried the latter first and was rather alarmed at the result. I couldn’t really get a picture, but basically I was getting fuel vapor in the intake, a feat that I did not think was possible. Ultimately, I decided it was probably the valve guide seals (which I have long suspected are leaky) allowing fuel into the valve cover, through the oil vapor recovery hose, and then back into the intake.
Then I went camping. Hence why my remaining time is evaporating at an alarming pace.
After that, I simply tried pulling the OVR hose off and IT STARTED! No idea what stars aligned but it started and ran for several seconds with me hammering on the throttle to keep it alive. Unfortunately whatever stars aligned to allow this to happen decided to bugger off, because after a little tinkering (in hopes of making it start better) I managed to revert to my former state. Undoing my tinkering did restore starting.
Mulling it over, I decided to go ahead and check the compression.
Luckily it was good. The plugs were a little grubby so I cleaned them and briefly set my hand on fire in the process. Woo.
I also managed to cross-thread #1 on re-installation. Go team! I think I got it in correctly, on retry, but it seemed VERY hard to thread regardless, so I’ve ordered a tap to further rui- I mean clean up the threads.
So now I am back where I was, except I have damaged threads on one plug.
Next up.... well I’m not quite sure. I’m going to have to give it a think. I am leaning towards an mix problem, but I have no clear idea how to test that.