Well, I have the doors off to go over them and replace the glass and weather stripping.
First, SAVE THE HINGE PINS! The parts supplies don't list the exact same one as on the trucks... so if you can, save/be nice to the pins as you bang them out.
My 43 is a typical 'wartime production' truck... no rubber, lots of felt. Felt is used it lots of places:
As vibration control between the door skin and the ribs, in the upper glass channel on the door, as the stop for the lower window position, and as the wiper on the outer window door lip.
Since felt is readily available replacing it should not be an issue. Only thing that is odd is that the felt is black, not the light gray I usually see.
The most expensive part of the window guide seems to be the channels in the door. $65+ per door. The ones I have are in good shape, so I will keep them. One place that I found that sells the channel (well, for 1950s on trucks) is http://www.showerdoordirect.com/ (just do a search for Chevy) for $25 to do both doors (vs $130) most people will never see the channels to begin with.
Good thing is that Chevys of the 40's sells patch panels... so fixing rusted out doors may not be a huge deal. But if you can find a good door for less than $200 it would be cheaper to replace rather than repair.