Hi Travis- From the pictures you posted, it looks like your ‘39’s windows were upgraded with ‘41-‘46 window frames (mine were, too!). Originally, ‘39 and ‘40 trucks did not have the metal frame around the door glass, which resulted in glass breakage. To accommodate the metal frame, ‘41-‘46 window glass is slightly smaller than the ‘39-‘40 glass, which is why I believe the ‘39 glass you ordered will not fit in your frames.
Here’s a link to an article that discusses ‘39-‘46 Chevy truck window glass.
https://oldchevytrucks.com/blog/2010/02/1939-1946-door-windows/Good luck!
