So, any lingering doubt I had about whether my flywheel was the source of the trouble has quickly vanished. Gunk everywhere!
Just a couple of notes along the way...
RUST SUCKS. By far the worst parts of this job so far have been getting the exhaust and driveshaft out. I think rust accounts for 75% of the time I've spent so far. As I posted earlier, my exhaust manifold/primary cats-to-midpipe flanges were seemingly fused together and did not want to separate.
The same thing happened with the driveshaft's universal joint connection to the differential flange: rusted together. It took two nights of soaking the area with PB blaster, and several hours' worth of heating the interface with a torch and banging away at it with chisels to get it to separate. The car's spent 9+ years of its life in the rust belt so maybe I shouldn't be so surprised. If you're in a similar boat it might be wise to get an exhaust shop to take care of the flanges beforehand (I'm going to try to get the studs out but failing that am going to just drive it to an exhaust shop once I'm done). And an induction heater (or something else more powerful than propane) might be a worthwhile investment.
I did ultimately manage to undo the driveshaft bolts/nuts without lifting the car off of my ramps to free up the wheels. But it was tight.
Doing this job at the same time as my PCV refresh/3IM swap was a good decision. Having the manifold out makes it way easier to get to the 12:00 and 1:00 bell housing bolts.
We'll see if I manage to put this all back together correctly.
After 14ish years of daily driver duty, my car's been mostly parked for the past year. I'm really looking forward to getting it back in action.
I assume it is normal for there to be some play in the diff? I could rotate my driveshaft slightly with the tires stationary... not much, maybe about 10-20 degrees.