A couple things come to mind and hopefully some other FTers will be along to answer.

At the very least you're going to be arriving in a different terminal than you'll be departing from, and that may involve reclearing security. If you have to reclear security your new itinerary is not going to work, even without bags, as they do not board up until the very last minute. I don't know if there is a shuttle bus inside the secure area, but even if there is your bags would need to make it to an entirely different terminal, along with you, and that won't happen if you have 40 mins to departure of your international flight. Hopefully someone that flies Alaska from LAX can advise on the shuttle bus in the secure area.

Have you asked whoever ticketed you if you can move to an earlier Alaska flight? That would seem to be the easiest solution. I had a change on an AA/Qantas trip coming up and received phone calls from both Qantas and AA, as well as e-mail from AA, so I'm surprised no one alerted you about the schedule change.

Some Qantas flights go out of T4 (AA terminal) and others go out of the international terminal. Alaska is in T3.