If you know you didn't fly BOAC or Qantas, and routed through Singapore, and didn't change carriers, then the only other contender would be Singapore Airlines.
Can't lay my hands on one of their 1974 timetables, but have got a link to one from two years later, 1976.
http://www.timetableimages.com/ttima...q76/sq76-3.jpg
Slight challenge is that the 4 times weekly service from Singapore to Perth didn't arrive on a Monday then, but this is the sort of thing that changes from year to year. In fact a flight does arrive very early on Tuesday morning at 0135, so if the officer on late shift didn't change their date stamp at midnight ....
The connection with this flight, assuming you didn't stop over, left London Heathrow at 1530 on Saturday, and the 747 routed through Paris, Athens, Bahrain and Bombay. These intermediate points did vary somewhat from year to year, but I think this gives a bit of a guide.
Blimey! A cellar full of old ABC guides your missus must be in a state of constant excitement!
My old ABCs (alas not a 1974 one) are in the attic, as we don't have a cellar. Mrs WHBM 
to whom I showed this comment burst out laughing !