Thanks catmando, it helps me a lot.
I have finally received the card I was waiting for, so I'll return to the drawing board soon.
First thoughts and main concepts :
I don't think I'll go with something that big, but the concept is there.
Total height should be 7.5-8 cm, more or less the original ST case + 1-1.5 cm.
On the front 1 cut for 3.5" floppy, 1 cut extra 3.5" space for ultrasatan or CF card, inside mount for 3.5" HDD, DMA-SCSI card, VGA card, extra poles for personal mounting board. Build in folded steel sheets 1.2 mm thick, powder coated, and bolt onto the original ST chassis.
I believe that a keyboard case with lighter folded sheets can be done too.
Sorry if I don't give news very often, I am doing this project on my spare time, so It may take some time.
But be assured that I will do it until completed, so it's not a kind of vapor project, as I want to build this case for my own use first
See you soon.