That compressor isn't clocked properly for a Fiero. You want one with the ports oriented like this:
It would have to be completely disassembled and resealed with new body O-rings. It would also need to be reassembled with the Fiero's 2-port rear head, to keep both switches. The one on craigslist only has one switch port. http://www.fiero.nl/forum/Forum2/HTML/124630.html
The pulley would also have to be swapped to a v-belt style, which isn't difficult with the right specialty tools. So would the clutch coil, or just swap the connector on your car to the new style.
It also DOES appear to be a reman-ed compressor, not new as advertised.