Why is the return line plugged off on an 83 F250?

Okay I'm really confused. I've got a 1983 Ford F250 with a 460 engine. There is a return line that runs back to the sending unit and it's plugged off before it gets to the sending unit. That appears to be something that a previous owner did. Well after taking the sending unit out it is also plugged inside the tank which appears to be from the factory. All the aftermarket suppliers of sending units have one outlet where mine has two, but why did Ford run a return line all the way back along the frame just to block it off? I think i can just remove the line and plug it off under the hood where it starts. I would just like someone to give me some insight on this. Thanks