Updates!
1. There's an entirely mechanical vent near the driver's left foot. I closed it. Previous owner broke the handle, so it was easy to close but will be difficult to reopen, but I'll build that bridge when I come to it.
2. Of the two ways to interpret what I said, I didn't mean the dangerous one. I guess there's no good standard words for the difference in turning the cruise on (as in, allowing the cruise system to work at all) and turning the cruise on (as in, telling the cruise syste to take over the accelerator).
3. I've taken a seat off its base and replacing those bolts is going to be easy. However, I'm still missing one more bolt *above* that level, where the bottom edge of the seat itself connects to its feet (which then connect to the base, the connection I was worried about before). I'm having trouble figuring out how to get to the top of that bolt hole without ripping apart the seat.
4. The holes in the floor below the rear bench seat go straight through to outside, no threading or welded nuts. I suspect the nuts were lost to rust years ago. The front two bolts for the seat just go through the body, and I got new bolts for those. The outer-front two bolts for the seatbelts also go through the body, same bolts as the previous two. The rear two bolts for the seat go through the body then all the way through a tubular frame member. I think it's meant for the bolts to stop mid-frame and have the nut put inside the frame tube, but I don't think I'm going to be able to manage that so I'm going to put a long bolt all the way through the frame there (the holes alreayd line up). The most difficult, which I haven't figured out yet, are the middle two bolts for the seat belts. They seem to be through some metal plates that are inside the van, under the carpet. The previous owner cut the bolts off, so I need to figure out how to get them out of there to replace them. I can't get below the body there because that's where the gas tank is. I'll post photos of that situation later and see if I can figure something out.
5. I figured out the reclining bench seat. You have to slide the seat fore/aft to the middle of its (short) travel, then lift it. Lifting it triggers the reclining action.
6. A few of the elastic bands have ends under easy to remove trim pieces. I'm still worried about how to get to the ones that are inside the other cloth/pleather bits.