As explained here, I'd install 8.1 and see what happens. But before I did that I would fix the video thing on the motherboard. Better is to put the old CC mobo back in and put 8.1 on it first, using a Universal install for any Mac.

I'm not sure if a SCSI CD drive is available or not.

The Mystic upgrade is not a rare upgrade by itself, so I'm sure others can relate their experiences.