They are slid too far up, and stick too far out.
Cut below the body line, make your joint about 3/4 inch below that line, unless the corner is too far gone. Less filler needed.
You will also have to likely grind the flange on the front side, they are too wide. The notch where it meets the lower rocker turn will also need to be deepened.
Completely remove the old rotted out cab corner up just below the top line on your replacement. ( make a 1/8" lap joint, way easier to weld to )
Scribe and cut part way around the corner ( flange ) at the front, finish with a sharp chisel. Drill spot welds, remove old piece of flange.
The corner should now fit tight to the body. It is literally cut and fit, and the more you fit it, the better it will turn out.
"Some modification required"