Looks like the 96 Stang Fuel Gauge/Sender is 14-18 Ohms empty, and 155-165 Ohms full. Looks like it would be a little inaccurate at E, but otherwise close if you used a digi cluster sender(8-12 E/155-160 F), referencing http://www.foxtbirdcougarforums.com/showpost.php?p=221798&postcount=3 . Your car is fuel injected right?
The speed sensor sits in the tailshaft of the trans were the speedo cable would be usually, and depending on your trans, you should be able to find one and wire it up rather easily. Since the gauge cluster is just information readout, it shouldn't cause any problems. You may need to do some soldering for the idiot lights, or maybe just repin the connector. Shouldn't be too hard to find a base stang cluster with just gas and speed. At most it would have idiot temp and oil "gauges" that only read via an on/off sender, like the idiot lights do.
Hope that helps!
..., this is starting to sound like fun!