The ZIP should be fine as long as it's SCSI and not parallel. The router could well draw 2.5A so beware. What's the 5V rating on the LC power supply?

The easiest way to go from internal SCSI to external would be to cannibalise an old external SCSI CD. You could score the power supply while you're in there.

Wait, isn't there an internal to external SCSI lead in the LC? Might need a gender changer or extension, but there shouldn't be a pinout problem.