Just want to update this thread. I called JAL and they confirmed that O class doesn't allow advance seat selection. So it's T-24 hours before I can select my seat. However, they were able to add my Alaska # to my account. I can't see it online for some strange reason, but the rep assured me that it's been added to my reservation. I find the website to be a bit awkward to use compared to ANA.
https://www.alaskaair.com/content/mi...er-overview:JL
O class gets 50% on AS.