Hi everyone, is 2h 50m enough transit time in LAX? International to International.

SYD > LAX Terminal B (QF17, landing at 16:10)
LAX > LHR Terminal 7 (UA923, departing 19:00)

I understand, I'll need to go through immigration, get my checked luggage, recheckin luggage etc..

Is 2h 50m sufficient? In the event that my inbound Qantas flight is delayed, and I don't make the connecting flight. Who do I go to at the airport to get rebooked on next available flight? I'm travelling in Premium Economy and OneWorld Sapphire, if this makes a slight difference?

Thanks in advance.