Jackbr,
Flew BA to Sydney in November 1988. Routeing was as follows:
Outbound, LHR-AUH-SIN-SYD.
Inbound, SYD-BKK-BAH-LHR.
All sectors were operated by P+W JT-9 powered 747's.
I recall that departure from LHR was late evening, around 2200L with arrival in SYD at approximately 0700L. Departure from SYD was slightly earlier in the evening, around 1900L, arriving in LHR early morning again at about 0530L. Sorry I can't be anymore exact than that with the timings. I'm afraid I can't remember the flight numbers either.