There is a golden rule about cab repairs on these trucks.
Start with the doors, then make the cab fit around them.
You currently don't have a good fit at the cowl, and your belt line doesn't match at the rear, and the gap widens along the window frame.
I don't see how cutting and welding the leading edge of the door will fix the issues of trailing edge of the door.
What I have done when facing this very problem, was to adjust the door for a perfect fit at rear (parallel gap, lined up belt line).
Then determine what the issues are at the cowl, then alter the cowl to match the leading edge of the door.
It is too late now, but the way to avoid this issue when replacing a cowl is to temporarily attach the cowl with little self-tapping screws, then install the door. This allows you to unscrew the cowl if the door doesn't fit.
Carl
