The locomotive in the background behind the Alco M636 No. 5502 in BHP livery, (8th photo down from top on this page) is an ex NSWGR 40 Class. The 40 Class was the first diesel main line loco to enter service in New South Wales on 30th November 1951. The class was obtained from Canada, where it ran as a switcher with a Bo-Bo configuration, but here they ran as Co-Co. Originally they replaced steam runnings between Sydney and Newcastle, often coupled in pairs. Here is a pic of class leader 4001, taken at Sydney Central during the Great Train Expo.
This livery was used on the Royal Train. The orignal livery when it entered service was green with chrome yellow lining.
Cheers, Gary.