Am not sure what year it is (84 or earlier), but you could check the PET katalog (link below).
https://www.porsche.com/usa/accessoriesandservices/classic/genuineparts/originalpartscatalogue/
I looked up for an early 3.2 and found 999-181-189-50, but PP shows it’s been superseded by 999-181-189-5A-OEM and ridiculou$ly high.
Pelican sells a substitute fuel line by the meter. I think the diameter is 14mm. The PET shows the lengths in mm by the way.
Here is a link that might be helpful.
Evaporator Tank Line
HTH