This week we enlarged the rear wheel wells to make room for the 40 inch tires. When we started the tires had not yet arrived in the mail. We clamped some wood to the axle to help estimate the size of the tire and to help draw the arc to cutout. We also deflated the air springs to simulate articulation (as if the tire was fully stuffed into the wheel well).
The original wheel wells were tall enough, but not wide enough, so the cutting was done on the sides (red circles in the picture).
The axle was not centered in the wheel well. It was closer to the front of the vehicle from the factory. So we only had to cut the inner wheel well on the side that faces the front of the vehicle.
We used some scrap aluminum that we had pulled out of the interior to make the covers for the cutouts. We used pliers and a hammer to shape it as needed. Then welded them on.
We primed and painted the cuts and welds and mounted the tires to check the clearance.
We still have to lift the front and cutout the front wheel wells before we can test it out. We will update the post once tested.