very little to no modification , there is a small bracket you cut off, and the felt window channel acts as a up and down guide. Be sure to grind down the overlap in the front portion of each door .
You have the ability to move the glass front and back and Im confident my window is in the center position to fit frame and I do not have any wind noise, lets just say if almost impossible to shut doors with window up, if your window is down you can feel the wind blast thru the open window!
Im very happy with the conversion, brothers truck has the best kit.
https://www.youtube.com/watch?v=CIjzwUBnsqs