There are differences. If it is a 390 car it likely has a C8ZE S1. If it is a Shelby or CJ it likely has a C8ZE L1 althouth I've heard of at leasts one coming with a S 1. It also matters were the car was made as San Jose cars have W MO on top tank and Metuchen cars, including Shelby have FoMoCo on tank. I'm not sure about Dearborn cars. Your best bet is ebay and likely it will need a core. The L 1s don't come around often, the S 1s are more common.