I have successfully used PCI or PCIe based 1394 cards on my last two windows computers to accomodate my Coolscan 4000. They are inexpensive and easy to install, and Windows automatically installs the driver for the card.
The Coolscan 4000 does not require power via firewire, so you don't need to hook up the extra power supply cable to the firewire card when installing (unless you have other firewire devices that do require power). The firewire interface on these old Coolscans is built in to the mainboard in the scanner, and seems to have a high failure rate of late, requiring very expensive repairs. Using a good quality 6 pin firewire cable and not providing power via the 1394 card will lessen the risk of frying the scanner's 1394 interface (I speak from experience on this unfortunately).
I also recommend skipping the Nikon driver x64 workarounds and using Vuescan for your scanning. Vuescan is much better than the Nikon Scan software.
DOn't you still need to do the x64 driver workaround anyway? It seems like you do to use it with Silverfast. Without the driver how does Vuescan recognize it?