You could change your current Ubuntu repository mirror and retry (apt update first). You can use apt-cache policy to check the troublesome packages and see what version are available and from which repository.
I was unable to find held packages, but you got me going in the right direction. For whatever reason, my sources.list file had a comment in it that suggested that because I used a smaller ISO it might not have been the full file. Perhaps a side effect of not allowing online updates during install.
So I got hold of a more 'full' listing of the official sources and ran apt update and it suddenly had way more packages to update and then the install script could find more of what it needed.