I decided to take a risk and sideload the update with TWRP.
Don't. It tries to update the firmware and fails, and KitKat fails to boot (you get coloured lines) because it does not like the firmware. My fault, I'll boot into TWRP, backup and re-run the 4.3 RUU.
Ok... This happened to me with TWRP (it fails with the m7 error on CWM). I decided to flash the stock recovery. Did the volume up and power button and went to install from phone storage. Went into the /0 folder and found a "sideload.zip". Flashed that. Rebooted phone and now I have the update succesfully!:laugh::good::good: