There's a fair chance that they'll have to reissue the boarding pass to you. Arriving at SEA is sort of like this:

Get off plane, go to immigration, wait for bags for 20-30 minutes, go through customs, hang left, go to the baggage check/transfer counter, then turn around and go to the security checkpoint and take the train to the appropriate concourse.

If all goes well, you should have enough time. Eastbound trans-Pacific flights sometimes arrive very early, and AS flights are occasionally quite late. It all depends, however, on whatever the airline gods have in store for you on that day.