1964 summer timetable shows BOAC Comets to Brisbane, but not on Wednesdays (your date) and not through the combination of stops described. Nothing too unusual about that, they all tended to get swapped around with each timetable change
http://www.timetableimages.com/ttima...64/ba64-19.jpg
Istanbul was an unusual point, it was never a mainstream BOAC station, but a BEA one (Comet 4Bs through Rome and Athens at this time). BOAC focus was through Cairo, but after the 1956 Egypt war BOAC were allowed to go through Istanbul, with traffic rights restrictions. Just a couple of flights left through there by your date, later they let it go back to just BEA again.