Fuel gauge hook up ....non stock gauge

If you have the stock tank and sender then you must match the gauge to it. You need a gauge for the approximate 9-73 ohm sender. GM uses a different range and some aftermarket, yet another.

http://www.stewartwarner.com/tech/faqSc.html

Here are some compatible examples from their catalog: http://www.stewartwarner.com/catalog/fuel73.html