new tank sending unit questions

[Crossram413]

Hi all,
So as expected the fuel gauge doesn't work after rebuilding the cluster on my 72 Rallye 340. I Did all the usual tests and determined the sending unit was bad. I now have a new unit and ground strap from Roseville which has 3/8" pipe and a second 1/4" connector.
The existing sending unit in the car has only one tube, 5/16" , so after I've read through lots of old postings on the forum, a couple of questions...

Is the 1/4" tube on the new unit a vapor return? Where would it go?
Do I need to do anything to properly connect the 5/16 to the 3/8"?
Should a 340 car have had 3/8" lines to begin with, and why no second line?

My engine is a 1970 if that matters.

Doug

 

[Old B5]

1/4" line is the fuel return. 340 cars came with 5/16 fuel lines.

 

[Crossram413]

Thanks, but I wasn't real clear on my main question. The sending unit currently on my car does not have a return. The new unit from Roseville does.
What should the fuel line setup be for my 72?