Well the parts (DIN41612 connectors) didn't arrive (still). I have some hope for tomorrow. I need to measure them and sort out clearances for screws in the front fascia.
In the mean time I have started a rough draft of dimensions above.
I also played with some rivnuts or rivet nuts. It didn't work out to well for M3 without the tool -
I tried to use a screw to compress the rivnut but the leverage of a M3 thread is to low and the screw head stripped so then I tried to compress it with a vice and it went bent ! :(
I will buy the too and try it.
I will first buy some countersunk rivnuts to try.