What were the lines originally? I'm pretty sure the '46 216 tank to pump line was 1/4" and the pump to carb line was 5/16" as I previously mentioned, but I need a need a confirmation of this as this truck had 5/16" tubing used for both lines. I know the '41 trucks had 1/4" tank to pump lines and I'm pretty sure the '46 was the same, wasn't it? The little flex hose (from the parts suppliers) from the tank valve has an adapter on one end to screw into the flare fitting for 1/4" tubing. That's another indicator the line should be 1/4" and not 5/16".
My son's 1946 2 ton with a 216 has 37,000 original miles and was garage kept it's entire life.
The patina on all the fuel lines matches which to me proves that they are original and never were changed.
The parts man, born in 1943, helping out in his dads auto parts store since he was 12 and is still there today.
When just this past week I went to buy the fuel hose between the tank and the fuel pump steel line I asked him for a rubber fuel hose. He did not look up the size, he instantly said they take 5/16" hose, how long do you want the hose.
Then I saw your post. So I measured the steel fuel lines from between the tank rubber hose to the fuel pump. Then the steel line from the fuel pump to the fuel filter. There is no line between the filter and the carb because the filter directly attaches to the carburetor.
All the steel lines were measured with a micrometer.
All the steel lines are 5/16".
It does not make sense to put in a 1/4" line before the fuel pump and a 5/16" line after the pump. 5/16 can not flow more then what the 1/4 is supplying it.