Use gasket rubber made for the window for mounting the window glass to the metal frame. You can use wood clamps with 2x4 at the top and the bottom to push the glass into the metal frame. Take your time. The side windows rubber gaskets have a long edge on one side that goes toward the outside of the window that will somewhat seal the gap between the bottom of the window and the outside of the window opening in the door when the window is closed. Don't forget the bumpers that fit in the little half inch slots on the inside bottom of the door window frame (if they are in the 39).
Restoration Specialties sells it, so do other places.
Brian