I went to check-in at the 36 hour mark. It was kind of weird because it would not accept my WorldPerks number as my identifier (choose one of WorldPerks number, credit card, confirmation number) but took the confirmation number ok.
Logged in and found the seat selector. I brought up the map for the first flight. I hovered over the priority seat I wanted, but no indication of selectablity was shown. Feeling brave, I clicked anyway. It gave it to me!
Moving on to the connecting flight, which was still 39 hours from departure, I was allowed to select the priority seat too.
The website then said that the procedure for checking luggage is either curbside or kiosk check-in. No waiting in the agent line should be required.
These were my experiences, as always, your mileage my vary. For those who have not had it work for them, feel free to ask me any question about how I did it. I did not try for exit row seats, just the seats that were blocked off for elite passengers at my time of purchase. Also, this is an award ticket booked online in case that matters.
Thanks for all your help,
Rocketman