[Lenovo P780] gonzo99:
Solved

Okay, I finally managed it, with a lot of research, cursing and luck!

In case anyone else runs into the same issue, here are the steps I took - I'll try to upload the files I used to this post later.

FIRSTLY: MAKE SURE YOU HAVE A BACKUP, PARTICULARLY OF YOUR IMEI AND NVRAM - MTKDroidTools is the best way to go, there are other threads on it.

It may not be necessary, but if it is, don't complain when you cat explodes and you spiral into a world of gloom and doom - BACKUP FIRST!

The key was finding a CN ROM that could be flashed using SP_Flash_tools on to a phone that has a ROW ROM on it. For my device at least (post April 2014 bootloader Chinese 'speed' version), none of the ones linked on here would work....

However, I found one on 4pda.ru that does work - The page is in Russian, but Google Translate does a reasonable job.

The page is here, but the direct link to the file is here The ROM in question is 'VIBEUI_V2.0_14​37_7.14.1_ST_b​y_sadist_v1.zi​p'

I also downloaded SP_Flash_Tool_v5.1352.01 from the same post, which worked for me, though other versions may work....

Pre Requisite Steps:

1. Make sure drivers are installed properly for the preload bootloader

2. Did I mention making a backup?

3. Extract the ROM zip to a suitable location

3. If your phone is one of the Chinese models after April 2014 (The date is on the battery on mine in the form: 140414), then replace the preloader.bin file in the ROM download with the 2014 version from here

4. Choose a suitable ROM for your device that can be flashed through recovery - There are several on NeedROM, personally I went with the AOSP-4.4.2-fix-PYRO_LS from here. Place this ROM on your SDcard so it will be accessible from the recovery.

5. Turn your phone off (do not plug it in yet)

6. Run SP_Flash_Tool_v5.1352.01 from the extracted file.

7. Click 'Scatter-loading' and browse to the ROM folder then load the MT6589_Android_scatter_emmc.txt file

8. Choose 'firmware upgrade' from the drop down list and make sure that all the files are ticked and the location field is filled in

9. Click 'Download'

10. Without turning your phone on, plug it into to your USB port.

11. The files should start downloading (First a red completion bar, then through various colours)

12. Wait until you get a green circle to show the download has worked. If you don't, then check the above steps again very carefully.

13. IMPORTANT - unplug the phone, then start it, while holding both up and down volume keys together. This will force it into TWRP. If you don't do this and let it boot into the ROM, then the original recovery will be reinstalled and you will have to start again.

14. You should get the 'Teamwin' logo, and then be in TWRP. It is the chinese version, but should be in English so no changes or translation needed.

15. Do a wipe (Not sure if this is essential but I did it) - The standard wipe is enough

16. Go to install and choose the zip you put on the SDcard earlier

17. The install should complete successfully. You may find it best to do another wipe (only minimum) here though I didn't.

18. Reboot and you should boot into Stock Android 4.4.2, with a few additions (Superuser is already installed - Lenovo Power Manager is added, etc.)

19. Choose your language and set up as you wish

20. Bask in the glory of a job well done.....

Troubleshooting:

If your phone does not flash correctly in step 11, don't worry. Make sure you have the correct files selected in Flash tools, and replace the 2014 preloader.bin if you forgot.

Press Download in SP Flash Tools again

Leave your phone plugged in, then take off the back and press the red reset button once. your phone will turn off, and then when it starts up it should immediately be detected and start flashing again.

If you never get the RED bar, then the drivers are not properly installed, so make sure that is done first. If you are on Windows 8, you will likely need to reboot into Advanced startup mode and disable Signature verification. There is a post on installing drivers that explains...

Hope that helps someone else avoid the hassle I went through. So far everything seems to be working fine and I have KitKat goodness without the Lenovo bloat. It definitely seems snappier and I can add the tweaks I want with Xposed.

If you like some of the Lenovo Apps, they do seem to mostly install and work fine on Stock Android, including the widgets. Props to lenovo for not needing their own launcher to work them!