High speed signals to FPGA
30 ns implies a corresponding wavelength of about 18 meters. If you don't make your edges too fast (say, target 8-10 ns rise and fall times), you should be able to route this a few inches without worrying about impedance matching.

I'd just use a ribbon cable for this connection. 

You will need a common ground between the remote box and the FPGA board. You can use additional wires in the ribbon cable to provide that. The more wires you dedicate to ground, the less cross-talk you'll have between your signals. Having equal number of ground and signal wires is safest, but probably more than you need. Having just one ground wire is risky. Somewhere in between is your optimum cost/performance point.