So, I'm continuing to backup the RecRoom PC today. I could have had it backing up overnight, but in my experience that's when something goes wrong.
Going to wipe both disk 0 and 2, which are both MBR. As it transpired, I had at least 800GB spare space on disk1, so that'll be the drive the Mint Distro goes on. I've been using the RecRoom PC as my main PC since I finished the masters. It didn't help having one of the Studio PC's drives dying, but I never really got back into the habit of using it again. But then I have a strategy of redundancy witn my PCs, which is why I'm only installing Win10 on one PC at a time. If any one goes down, I have others to use!
Also I discovered that program that no longer works on the Media PC, also no longer works on the RecRoom PC either. It was old kit and no longer being developed so its time has come. There may be others that don't as well, but hopefully my Adobe CS6 pack will.