As far as I know there are 'custom' one piece window kits available,but I'm not sure if you can retro-fit earlier pre 51 door glass. Maybe someone out there will chime in?
Try clicking on links and have a nose around for electric window kits there are several vendors who do them.

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.