these 4-way level shifters, and put them on a piece of veroboard with connectors for the Xilinx board and a 50-pin ribbon cable.
The 50-pin ribbon cable terminates in an HD50 connector (commonly used for narrow SCSI applications) on a PCI bracket. The panel has been fitted with the same connector, so a SCSI cable can be used as an interconnect between the PC and the panel.
For now, I've put the top cover on four standoffs. I just daren't put any real load (like the console typewriter) on top of it now.
I'm going to create some extra space in the top of the case by replacing the video card and cpu cooler with low-profile ones. I can then mount the Xilinx card horizontally above those components, using a flexible PCIe extender, similar to this.