Comment # 14 on bug 1179387 from Stefan Dirsch

Ok. I have no idea, why there is no single framebuffer mode available. There
should be with kernel boot options

   nomodeset vga=792

BTW, this GPU is from 2002! And it's an AGP card! I would guess the Matrox
G400, which appears to work,  is a PCI card.

What about combining your machine with a CRT monitor from 2002 and be happy
with 1024x768 in framebuffer mode. ;-)