It started on 30th August 1979. The day before, its Newcastle service was launched on 1584, which moved to 1413 (the old 2KO frequency) on 29th March 1996. I remember SBS started its 1035AM service in around late 2005. Its 1485AM service is still on air to this day.
As for the 603AM ABC Nowra service, that was launched on 31st January 1989 as an RN service, whilst 2WN became 97.3 ABC Illawarra on 15th May 1991, after WIN had vacated the VHF 4 frequency on 31st March that year. At around the same time, ABC FM (now ABC Classic) moved from 107.9 to 95.7.
WIN vacating VHF 4 allowed the launch of Power FM in October 1991 (nearly 30 years ago now!), as well as the FM conversions of 2OO (i98FM) in June 1992, 2WL (Wave FM) in July 1992, 2KA (One FM, now The Edge) in October 1992 & 2WS (now WSFM) in June 1993.
Sources: SBS, ABC and Department of Transport & Communications’ annual reports