Ok, I am nearly done.
I purchased a SCSI2SD board, extracted the x68000_V4 hard disk image on it (SCSI ID=3), installed everything in the x68000.
Then I wrote the Masterdisk image to a floppy, booted with it and then used:
Now when I turn it on, the bootloader starts, but it doesn't detect the HDD (all 8 SCSI IDs look empty in the boot screen) and so it doesn't boot from it.
Interestingly though, booting from the Masterdisk and typing C: the hard disk is there!
I can navigate the folders, launch tools, etc.
So the setup (SC card image is proper, SCSI2SD setup, installation, power), is all fine, but no sign of the drive at boot.