This is strictly from experience dealing with these bikes and parts - I'm not an expert or professional with saddle restoration. I'm talking here about the "tourist" or lightweight-style saddles from the 1940s. Some of the bikes had saddles from balloon tire bikes, which are a different animal.
The covering material was often called "fabrikoid" - a way of applying a spray to cloth to give it a leather-like appearance. It started with luggage but proved quite popular. It usually dries out and is brittle after 70+ years. I wouldn't put a whole lot of miles on an original saddle. The base material varies. Usually there's a layer of cusioning horse hair or other padding and a metal pan. Sometimes you have a heavy-duty leather layer in there as well. They vary somewhat, but I would deem the materials to be on the "primitive side" - cloth fabrikoid, horse hair, leather padding, batting, etc. Again, none of this gets better with 70 years of age - it all dries out. Some saddles have a solid metal base plate, others use springs in a hammock fashion.
The one constant with the "tourist" saddles I've seen is that they're uncomfortable by 70 years later. I did come across a couple 1950s-60s era saddles that were a bit better. But the early stuff from the 1940s was universally bad - very dry, very hard, or simply mis-formed with age. Some of the saddles are fascinating - slide rails, tornado springs, etc. But they're period pieces and something to keep with the bike rather than to ride. Even the ones that looked nice did not ride very well. I don't own a single one of the period saddles any more.
Every bike I own today, except for one, has a Brooks saddle on it (I own one ballooner, and that has a Troxel long spring - but different animal again). The Brooks B66 is my suggestion for a rider saddle. Save the original ones to complete the bike, but ride something newer and which you can custom break-in.