Hi Rod
Thanks for that. I gave up in the end. I'd checked and quadruple checked the files were in the right spot, reinstalled ZenCart twice and even went through the folders of my old ZenCart website and made sure all the files were in exactly the same places - which they were. So I still have no idea why it wouldn't display the AustPost option in the shipping modules.
Eventually I just copied my existing ZenCart site across to the new server, and started tweaking it there to create my new site.
That worked.
One day of my life down the drain....