Stuck in the lift channel or stuck in the door channel? You will have to drop, tilt and remove every fastener in the door to get the glass out of the door. The lift channel comes out with the glass.
This page and the one before it are helpful.

http://chevy.oldcarmanualproject.com/shop/1947truck/47ctsm0104.htm

Getting the glass out of the lift channel...use the above tips, and take your time.

Steve H