You'll need to be on stock (unrooted) LJC to do the update.
Also... for now if you want to re-root:
1) Install custom recovery of your choice
2) Flash the following .ZIP:
...and you'll be all set.
I'm hoping to see a full TAR available soon where we can make proper one clicks.
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If you like the AOSP efforts and want to help get new devices on board, donations really help.
Current donations will be going to help ETF the spare line I'm not using.
Please continue to thank and support those who bring these great things to our devices!