67-72 fuel tank sending unit question

[72freak]

I have always seen advertised V-8 sending units and 6 cyl sending unit. V-8 being a fatter fuel line and fittings. I am needing a couple so I have looked at my collection of trucks and the big block Longhorn has a big line sending unit (new) but all the rest of my original V-8 trucks have a smaller one. I know the trucks are original V-8 trucks so whats up?

Now....if you look in the LMC cataloge they designate 2bbl v/s 4bbl. instead of the V-8 v/s 6 cyl. That would make sense because I know all the trucls I have that I looked at were v8 2 bbl trucks and the Longhorn is a 4bbl.

looks like the big line is about 3/8 OD and the smaller line is just over 1/4.

Can anyone shine some light in this? i tried calling Christians trucks but all the phone numbers were not working.