Seating
Front Seats: Manual and electric, some enterprising individuals have converted to a bench, others have added a jump seat between the two.
Second row captains chairs: Use a different mount than the benches, not interchangeable. Some have cut out the mounting from the junk yard and welded them in place to install a bench seat. https://www.astrosafari.com/threads/how-i-installed-a-stock-bench-in-my-cargo.92889/#post-905633
Bench Seats: All of the bench seats will fit into the factory floor anchors across the years. However, you should watch as there were some changes over the years as far seat belt mounting. Also, in 2000(US/Can?) they added the Child Safety Seat Top Strap Anchors. Astro/Safari Van Generations
Second row bench seats are different than the third row in important ways.
A. Second row seat has a passenger side armrest(even on standard bench seats) because of the gap between the seat and the sliding door
B. Second row seat has the attachment point(Latch Plate) and guide for the passenger side seat-belt, which won't be there on the third row seat, so if you want to use all three available seats in the second row bench, get a second row seat for the second row.
Older seats will fit into the slots on the floor, but watch the seat-belt configuration on the really old ones. The newer ones(2000 and up?) have a top strap latch system for child safety seats.
Armrest Repair:
It's extremely common for the armrest locating pin to break off, causing a floppy armrest. It's really easy to fix, you simply remove the armrest, drill out the remnants of the locating pin, install a properly sized nut/bolt combo and reinstall the armrest.
Swivel seat information:
WinnieVan over on AstroSafari.com is in the process of creating a fantastic swivel seat for our vans, using the stock seats. They are about $400 for the passenger side. https://www.astrosafari.com/viewtopic.php?f=69&t=144642
Another Swivel seat example using https://amzn.to/3HqFGRT: https://web.archive.org/web/20190716161955/http://www.vanningheretothere.com/swivel-seat/ but it seems the pictures are gone.
Robust DIY swivel seats: https://www.astrosafari.com/viewtopic.php?f=13&t=8236 another one of the same https://www.astrosafari.com/viewtopic.php?f=127&t=8455#p91271
https://www.astrosafari.com/threads/swivel-seat-install.142050
https://www.astrosafari.com/threads/swivel-seat-base-fabrication-todays-project.142436
https://www.astrosafari.com/threads/a-not-too-expensive-seat-swivel-base.65794/post-632241
Aftermarket Seats(conversion vans):