You did not mention a year but most of the metal lines from the tank to the point where it connects to the short rubber hose between line and fuel pump is 5/16". The rubber hose should also be changed and postwar hoses are repro'd by one of the Packard Club regions. Any year hose can probably be made up by a local parts store or hydraulic place -- most likely with different looking fittings though. Note there are different versions of the hose so if you order a repro make sure you get the one correct for your year. 22-23rd series models seem to be a time where there was a bit of either version mixing.
If Classic or one of the other tube making places cannot help with a premade tube, many of us have bought a length of
copper-nickel tubing or brand name Cunifer tubing (often sold for brake line use) for this purpose because it is much easier to bend, form, and then maneuver into position around the obstructions at the front suspension and radiator areas than the original steel line. The tubing is often available locally and is also sold at many of the online parts and streetrod stores.
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