Sorry it took so long.

Original removed windshield and the truck it was removed from:
Windshield top to bottom = 15 13/32" (the edges of the windshield glass are slightly rounded).
Windshield side (face) of pinch weld top to bottom = 15 30/32"
Difference = 17/32 = 0.53125
Div. by 2 = 0.265625 = tight, if expecting 0.5

I used a right angle held against the pinch weld and pushed to the top.
Same on the bottom pushed down.
Measured with a scale from the right angle edge to right angle edge.
Even with all this hoopla, paint, rust and unevenness of the window channel....

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."