Remember that you'll get on before most other people so you'll prob have free run of the overhead storage before anyone else. QF tend to keep the bassinet rows (ask for/book them, if you haven't already) open as long as they can, so there's a reasonable chance depending on load.
The nice people over at the
Qantas forum can tell you what the load is like at the moment if you let them know which flight number/s and the dates, and show you how to check for yourself. And I suspect a Mod will be along to move the thread there shortly given most of yr questions are QF-specific.