Agree. Even 90's Magnum engines had a 5/16" tube. I think only a few cars have a 3/8" tube. Later Corvettes do. If installing EFI fueling, most people run a new 3/8" tube and use the factory 5/16" tube for return.
I heard even the big block cars ran 5/16" when I had mine out I decided to upgrade to 3/8" because I heard it helps keep the fuel cooler plus I went with a 3/8" sending unit with the return line nipple so if I go with fuel injection its there if I need it.