General Motors made it very simple to replace the two small windows in the rear doors of these years.

Simply place the rubber seal (now available from full stocking early GM Truck Dealers) around the pre-cut glass.  Press into the inside window opening. Three special clips secure it in place. It could not be easier! See Photos.

Oops, one big problem. If you don’t have the special clips, Good Luck!
This 1941 Chevrolet Panel Truck owned & totally restored by Jim Winters, Rochester, Minnesota.