My first thought was, "David McKay"!
David did not enter this race and was awaiting delivery of the car Jack was driving in this event. I have no idea of why he might have been trying out Youl's Cooper, but it does look like him.
I did e.mail Geoff Smedley about it, but he didn't respond. He's too shaken up by the news that Symmons Plains has been offered for sale for subdivision.
The same photo in cropped format is on "Old race pics".
Its shown as John Youl and sure looks like him.
Ellrosso may have some info on the shot.