I used to do body mount chops for locals and since there's always the chance you might go bigger in the future I would clearance them for 35's as I had for my FJ. The chop is a bit more extreme, but you dont lose any strength and you'll never have to worry about cutting more later if you change you mind on the tire size when it comes time to buy the next set.
Here you can see where the tire was rubbing (this was a 285 tire)
Because it was this close
and this is how much extra material the original body mount is equipped with
This is how much you want to remove for maximum clearance; cut vertical inside of the centerline of the bushing at its most forward point, and horizontal along the top edge of the mount around the radius of the bushing, and about 1" on the front inside toward the frame.
I hammered the leading lip in under the top area and ground it clean in prtep for the weld
Then weld on a plate to the leading egde and stich about 3/4" at the top. Now hammer the remaining plate around and stich some more until it meets the back of the original mount, then weld down the back. Notice I also stayed above the factory lower lip line as this area is the most prone to rub
Now just paint and you have maximum clearance. This is the tire at its closest point to the mount and nowhere close to rubbing
This is the view from underneath, you cant more clearance without cutting the actual bushing away
Hope that helps anyone who plans to go maximum tire size... One of the trucks I did had 295 tires with no lift and after doing the extreme chop it had no rubbing - it gives you a lot of clearance at the most crucial area.