The concert with the most number of top groups on the one bill I went to was Randwick Racecourse in the early 1970's, during the day/afternoon featuring (in no particular order)
Manfred Mann
Deep Purple
Free
+ supported by Aussie band "Pirahna". What a day!! Got me into music big time......
PS: The Led Zeppelin concert in Sydney was amazing as well & to get a good view as I had to climb a fence and sit on it for the whole (lotta love) time. Worth it.