Have tried to research this a bit and found the following links which may be helpful in the ID these fossils:
Second photo - This academic paper A new species of Atlantidosteus LeliÆ¨vre, 1984
(Placodermi, Arthrodira, Brachythoraci) from the Middle Devonian of the Broken
River area (Queensland, Australia) - this paper has some some photos of a 'suborbital plate', from the cheek of a fish with similarities to those from Homostius
I also came across the following link which indicates these bones are likely to be highly radioactive, so just as well I left them for others to enjoy viewing!