Thanks again for all the great info here, @kev. I got my parts; all the fasteners I pulled are in individual labeled ziploc bags, and the ones that the previous owner had already pulled before I got there are all mixed together in another bag. I seem to have everything, at least I haven't found anything that I'm missing yet.
The square plastic inserts for the A-pillar trim are really hard to remove without damaging them! I managed to get one of the four out cleanly, the rest I broke, or were already broken. The white plastic inserts for the seatbelt mechanism in the door were tough too; I got one of those out intact, and figured that was good enough. Since I have one good example of each, I can 3D print replacements for both of them.
I tried to pull the belts out of the reels to inspect the webbing, but it seems like they're stuck. Is there a trick, or is something broken?