the wiki at the top of the
Airbus Reconfiguration Thread shows which jets have the cabin mods
use
FlightRadar24 (just put ASxxxx at the end of the URL in the address bar when the link brings up the FR24 page) ~40-48 hours ahead of your trip to see the assigned jet ... there's of course some chance of a tail swap, particularly if there's a SEA overnight involved before your flight