Fuel tanks

Does anyone know what the difference is between the early and later A body fuel tanks? I recently purchased another early dart and the tank is rusted out, will a tank from a 68 work are the fuel filler necks different. I see there are two different grommets available for early or late, but some places list the tank as being the same part and others as not. I have a 68 tank and would like to use it if possible, but I only have the filler tube from a 65 dart.