I am doing some ignition mods - and I need any experience regarding adapting 10mm to 14 mm plugholes .
Further - the project already has a very short 14mm hole - so a simple adapter (14mm to 10mm) is feasable and and if there is an existing product available , I will get one.
I have already looked at plug saver - heli coil .
It looks like a very well machined steel insert with a tiny upper lip will do the job .
I accept that a spot face on the upper surface may be required.