I think Junket is right about Chevy being 0-90 ohm - Most Cobra replicas with Smiths are set up for the Mustangs around 1990. Their range is 16 empty to 168 ohm full.. If right, actual full would be between 1/2 and 3/4 on guage, while empty tank would be below empty on the guage. Nisonger, here:
http://www.nisonger.com/
can probably adapt yours to the correct range.