Which external electric pump?

To be honest where is the return line on these cars? I know two lines come off the tank but there is only one line on the carb or anywhere on the motor. My uncle had this pump on his 68 Dart drag car for 7 years. Then prior to that he ran another blue pump on the street non stop with no return line. I am not trying to sound like I am a jerk because I am not and all info is welcomed. Just trying to learn more and more bout these cars overall.