Any sign of a frame number?
The components are obviously of later origin.
GB Hiduminium calipers are post-war, the saddle does not have the oval Brooks stamp, the headclip arrangement is suspect, the handlebars do not have the distinctive pre-war swoops we associate with Oppy, (as seen in this poster)
In a most uncharacteristic fashion, there are no photos of Oppy's feat in Australian newspapers.
They referred to his bike as a Malvern Star.
It has been suggested that it was a BSA branded frame that was used when in Britain.
One identified backer was Cyclo Variable Gears and in the catalogue found on Disraeli gears has this image
Bruce Small, who ran Malvern Star was also trying to secure BSA supply contracts, and this may have influenced the branding.
I will ask to see if there are any known photos of the epic ride to clarify the brand name on the frame.