Without having spare parts, like NuBus graphics cards, NuBus SCSI cards, spare RAM, spare hard discs, I would suggest that you get your motherboard recapped. There are a few in the Fora who can and will do it.

btw, the PDS slot (the one that looks a bit like a 64-bit PCI slot) *must* have something in it. personally, i have a sonnet crescendo g3 400mhz in mine. the faster 24-bit nubus cards run well in these systems.