Probably the same source that informed me of the same thing a few years ago: when it arrived at its new home, I was contacted via the Tank Museum and asked if I knew anything about the 'Grant modified for the atomic tests' (since I'd written about the tests in relation to Centurion).
On being shown an image, it was obvious it was the Malkara observation platform, the provision of which was covered in the Malkara papers at NAA, and is the vehicle visible in several images of the Malkara testing at Woomera.
We have all heard (and to my sham, believed!) 'furphies', Doug: a forum like this does help to dispel them.
Regards
Mike