The AA rules state that you do have access to first class lounges operated by One World carriers when travelling internationally on a One World carrier as a One World Emerald (which maps to AA Platinum Pro). The fact of your travels being in J vs. Y is wholly irrelevant. The fact of you departing LAX on an AA domestic flight as a AA elite does not invoke the AA One World North America exception policy as that policy applies only when travelling solely in North America. So, the rules are clear that you do get QF LAX F lounge access in your situation.

The only hiccup is that the rules are stated without such self-evident clarity that an average airport lounge worker would be guaranteed to interpret properly. Further, QF F lounge has been known to not follow the rules. So, just be prepared for a fight (with the knowledge that you are in the right).