Hm. PDS to PCI maybe. Nubus to PCI sounds like pain.

Drivers, sure, but you've still got to get the 68k Mac to recognise the existence of the PCI controller. Or fool it into thinking it's something else. And then get the device drivers for your PCI card to load onto a 68k Mac, and run on a 68k CPU. Considering there were no 68k machines with PCI, I'd be willing to bet all the drivers are written for PPC.