... 2 years, and a company move later:
I've managed to get SCO 5.0.4 running in a VMWare workstation. The trick was to use an IDE disk, and not Buslogic... I wanted Buslogic in case I ever wanted to import it into ESX, but a workstation will suffice in my case.
I booted the system with the 5.0.7 install floppy (downloadable from SCO), I mounted the 5.0.4 CDROM and installed it without any problem. The only issue I had was the network card (autodetected during installation) not being present in the kernel. Had to relink it afterwards.
Thanks all, for thinking along with me.