0) Install and set up MultiRom Manager
1) Download image
2) Copy onto device
3) Boot into Recovery
4) Backup > Select system and boot
5) Go back to main recovery menu and check the "Restore" section to see if the backup ROM is present
6) Install > navigate to the luneos grouper zip file, uncheck "inject MultiROM after installation" and swipe to flash
7) You may get a message saying "no OS installed" and another "not set as root". Ignored both messages and reboot.
8) I got fed up of waiting and turned off during the Google logo; however, after rebooting the device and waiting for ages at the Google logo, some minutes later the LuneOS logo appeared and the OS booted up!
But! There was no virtual keyboard... I couldn't get fingerterm to load, and bluetooth wouldn't load, so I had no software or hardware keyboard. Consequently I had no way of entering the LAN password, and thus no way of pulling any new packages that might have helped solve the problem. Oh dear.
Worse, the system was fairly slow to respond, and after several attempts to get the above to work, I ended up ditching the OS in the end, rather than pursue further to see if the keyboard worked in a nightly build.
(LuneOS Version 38 build 286)