Are we absolutely sure this was an RB-211 powered aircraft? The last time I flew Qantas SFO-SYD, last year, the equipment in use was the Extended Range version of the 744, a 747-438ER. Judging by the length of the (very comfortable) journey, I think I worked out why.
And the engines on VH-OEH were, I think, General Electric CF6-80C2B5.