[Steeveedee]

Yes, it is the wrong carb. It's not calibrated for a 305 if it's for a 454. That said, unless it's leaking in some obvious way, I'd wait on finding a correct one. Let's see a pic of the carb. It's possible that there may be an open port on the carburetor, since later engines had emissions equipment that connected to the carb, and your truck doesn't have that. Your fuel smell can be as simple as a bad gas cap gasket, btw. Is it a locking cap?