Since I wrote the above post, I have taken apart my '46 passenger door and sure enough, the window channel only extends up to the point where it would begin to curve over the rounded part of the glass. It is held in place with a tiny counter sunk, slotted screw on the straight or rear part of the door. On the curved or front part of the door, there are two of these screws. At the bottom, the channels are held in place by a flap of metal you bend to hold the channel.
The interesting part is that above the window channel felt it had a rubber weather stripping in it. It was decrepit after all this time so I don't know if it started out contoured to fit the rounded edge of the glass or if the constant pressure of the glass shaped it over the years.
