What's the difference between 71 Dart and 72 Dart fuel line?

You didnt mention what engine, im going with a V8.
From the tank to the fuel pump, they should be the same.
Ask them to be sure.
From the fuel pump to the carb, it would depend on the carb.
Obviously if you have a Carter/Edelbrock, you would order one for that.
Thermoquad, you would order one for that.
If you ask them, they will bend you up a 3/8" fuel pump to carb line.