The instructions for the installation of the expensive Rally Armor flaps are on their website. You can see the mounting points. You shouldn't need to cut anything to fit, there's plenty of room in the wheel well.
I don't know what if any mounting hardware you have, but you may need to make some brackets.
As far as the instructions for the $140 flaps goes,
There are 3 points on the wheel well in the front for the outer mount points, and 1 point underneath that a bracket links to for the inner mount point.
Also in the rear, there are 2 points on the wheel well for the outer mount points, and 1 point underneath with a bracket.