With a 12" lift you will still need to do some cutting. As the width of the tire will still cause you some clearance issues while turning. The outside of the tire will swing in a wider arc than a tire that is more narrow. Usually the problem is at the rear of the front wheel well, where the fire wall is. I used to run a 10" lift and 39.5" Super Swampers on a 16.5" X 14" wide wheel. Even with cut out Bushwacker fender flairs I still was making contact with the rear portion of the fender well. A three inch body lift was also installed to help with the contact problem. On a side note the truck was not a practical wheeler, it was used for mud racing and that was the extent of it.
LT.