I just had an interesting chat with the Reverend Canon David Elliott Courthope Lewis who is/was 2nd cousin of Gavin and John Youl.
BTW: His grandmother was Lina Henrietta Youl who became Lady Lewis, the virtual matriach of Hobart for many decades. (Phew let me catch my breath!)
Rev. David was close to the boy's father Boyce as Rev. Lewis was based at Launceston at the time, and he told me the story of what prompted the family to build the Symmons Plains racetrack.
Apparently the family had leased out the edges of the property along the main roads for billboard advertising (such as "Try XYZ jam - it's the best!") as many pastoral landholders did. Not only did they receive revenue from the company, but they also received incentive payments from the government to assist in the growth of Tasmanian businesses.
Now with a property that had grown in access of 2,000 acres at one time, with many main roads interweaving the "Symmons Plains" holdings, that came to quite a nice static income.
Then in the late 50's the Tasmanian government decided to not only stop the incentive payments, but put in an overall ban on advertising billboards (except those involved in specific locational tourism activities).
This was a loss of a sizeable income, and apparently Boyce, Jack Brabham and the boys were together at some stage and Boyce was bemoaning his loss, and together they came up with the idea of laying out a racing circuit in a suitable part of the property. So it happened.
There may also have been some recognition that Longford's life was certainly limited with the speed of race cars increasing.
Now I may expect some response such as "nah - that's not what happened!" but it may well be an interesting part of the process of the establishment of "the Plains".
Cheers all.