You peaked my curiosity a bit - I didn't know (or at least didn't remember) that Ansett had gotten a flight engineer station. I did recall that the launch customers were all USA operators (United, Delta, and American) and that per the original FAA directions had ordered a 3 crew flight deck. However other operators were at least interested in a 2 crew layout so Boeing was already working on EICAS and the associated changes to make it 2 crew. When the FAA report came out that OK'ed 2 crew, the launch customers all immediately wanted it - even with the 1982 price tag of over $500k (at the time the story was they'd pay that back in less than 2 years). The first 767s were built with 3 crew flight decks (memory says it was the first 7 or 8 off the line). The first 767 to fly - VA001 - had the 3 crew layout throughout the initial 767 flight test program, but the others were all retrofit to 2 crew (before they flew IIRC). VA001 was eventually retrofit to the 2 crew layout after the original 767 flight test program was complete.
I did a little checking - the first 767 for Ansett was l/n 24. I'm guessing they had originally placed the order for a 3 crew 767 - and due to their other agreements decided against paying for the 2 crew upgrade. So Boeing had to come up with a hybrid 3 crew layout for one customer. I'm also guessing much of the 3 crew kit that was removed from those first 767s was re-tasked for the Ansett aircraft.
Operators really liked the 767 - it was clearly better than the competition - at least until the A330 came out - and would fly forever with minimal maintenance (there are a lot of 767s still in service with over 100,000 hours) and was popular with passengers.