Getting the case back from the painter seems to take longer than expected, hopefully during next week...
I have made a temporary backing plate for the KB:
I have four bolts attached to the case and will clamp the KB between the case and the backing plate.
This plate is made of hard board and a girder of aluminium. But I'm working on a plate in aluminium with a thin foam sheet to protect the PCB.
I read through the whole thread before I wrote this and I'm impressed and humbled by all help you have provided during this project. Thanks so very much, couldn't done it without you.
Edit:
I promise to write a longer and more well organised article in Modifications thread when this project is closer to completion.
It feels a bit ill-placed now, albeit not from the beginning.