Hi
Michael and
grumpy,That ties into the info I have also...
The proprietary company Rover Mowers (Australia) Pty.Ltd. aquired Scott Bonnar limited in 1980 with Rover as the major shareholder. An export division was left in Thebarton, South Australia until 1983 when the factory closed and relocated to Brisbane.
In 1981, the new company was named Rover-Scott Bonnar Ltd. and was so named until April 1992 when the name officially changed to Rover (Aust) Ltd. They were still producing machines badged Rover-Scott Bonnar at this time, as far as I am aware.
I am led to believe the first machines badged as a Rover were produced in late 1992 or early 1993, but I have been unable to substantiate this, as my records don't have an exact date for the change.

Thanks to Michael, 1993 looks very much like the year of the change.