OK, I think (but im not sure) that the combo can be done, but it may take some machining. The 4.2 crank with the 4.0 rods will clear, but not by much. The high lift cam will open the valves too far, and it will make contact with the pistons for sure. I would suggest boring it out, and keeping the factory crank. If you have your heart set on the 4.2 crank, recess the valves or get a long duration cam with a low lift. In a little while I can get more info, because a friend of mine bored his out to 5.1L!