Welcome to Stovebolt Backets.
I agree with the rest of the guys that original factory fuel lines for your '41 were most likely pre-bent steel and the materials for replacing them at the time in the Master Parts Books were just the easy way out for making up replacements when needed.
I did a bit of snooping through various resources and found nothing that specifically states that so far. Even the original
1941 Chevrolet Truck Data PDF from GM doesn't discuss fuel lines. The specifications of the 1941 Truck fuel system are in the first pic below, taken from that PDF.
On your related question on the flexible fuel/oil lines listed in the Master Parts Catalog, the same hose assembly (GM# 592818) is used for both the flexible fuel line attached to the fuel tank output shut-off valve that connects to the fuel line going to the pump and on 1934-39 vehicles with oil filters as the inlet line. You only need the one for your truck for the fuel line connection. It's also my opinion that there should only be one (1) flex fuel line for your truck. The catalog shows a quantity of two (2) in the Parts Group 3.163 section (see 2nd pic) for some unknown reason, but later in the catalog under the truck specific Parts Group 16.000, it's listed as a quantity of one (1) (see 3rd pic).
Just IMHO, but I would go with the pre-bent steel lines as I think you will find them accurate in appearance and design and definitely the flex fuel line assembly..
