Quite right Qantas operate their 747-400's in two configuration types.
VH-OJA, OJB, OJC, OJD, OJE, OJF, OJG, OJH, OJK, OJM, OJN & OJO 14 First, 65 Business & 315 Economy
VH-OJI, OJJ, OJL, OJP, OJQ, OJR, OJS, OJT, OJU, OEB (ex Asiana), OEC & OED (ex Malaysian) 14 First, 79 Business & 265 Economy
The first group known as Kangaroo Config, and the second group known as Pacific.
The Pacific Config aircraft tend to operate all non-stop Sydney / Melbourne to Los Angeles services, while occasionally Kangaroo Config'd aircraft operate services via Auckland.
Kangaroo Config'd aircraft tend to operate all other services to Europe, Asia, South Africa & South America with the aid of spare Pacific Config'd aircraft
Hope this help's to answer your question