Firstly a massive thanks to RyokoN and - much more of this is their work than mine.
The end result is unbranded UK firmware (no docomo/jp apps etc.) 14.2.A.1.114 with SuperSU and NUT's Dual Recovery. The bootloader of course remains locked.
Just a simple guide to update to the latest JB firmware (10.4.1.B.0.109) on locked bootloader. The customisation is Generic UK.
Please note that this is only compatible with the SGP311 model of the Tablet Z, and requires that you are already root...
Created with the usual method
Thanks for all your job!
Please make rooting method for 4.4.
I've just received the update in PC Companion, will cook something up tomorrow if I get a chance
(Decided I can't be bothered waiting for OTA :P)...
Here are the necessary files for both a wipe and non-wipe update: (wipe procedure identical to OP, non-wipe procedure identical to Z1)