Sorry about that! Figured it out, I just re-downloaded the file from the app store and it seemed to of work. Everything's up and running it seems. What would be the best way to clone the drive in case a update breaks everything? Ideally something that can backup remotely?
So I've launched into the Unibeast installer for High Sierra.
When I hit "Install MacOS" the continue button goes gray and nothing happens? I am using a 8300 USFF. I have upgraded to the latest bios recommended in the first page and confirmed the bios settings.