I admit I have little experience with the 'later' 2 piece door glasses, but I imagine you will have to remove the vent glass and channel to allow the new glass to drop into the door.
Most vehicles of this era are pretty similar.
Someone with more definate info or pix will chime in soon.
Jock thumbs_up

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.