I never knew of this aircraft but found some Hansard records of Australian parliamentary debate and speeches in late May and early June 1970 regarding the aircraft's demise. According to these a grand total of 30 aircraft at most were anticipated, pending the feasibility study with British Aircraft Corporation. Significant factors were brought up by the then Liberal government (PM Malcom Fraser) as to why the project should NOT proceed:
1) The RAAF current experience in the Vietnam War "..demonstrated that for close support operations helicopter gunships had many attractions".
2) RAAF requirements for a supersonic trainer could be achieved by "..specially equipped dual-control Mirage aircraft would deal with this requirement."
3) Little to no potential of overseas sales.
4) The feasibility study was just that. According to Sen. K. Anderson (Liberal Party) - "...the purpose of the exercise was not to design a specific aircraft but rather to study the feasibility of a particular design concept and the market it would attract".
There's several mentions of a "Project N" production go-ahead that seems to have some indirect bearing on the matter. I'm ignorant of that one.