The 08 5.4 didn't have the two piece spark plugs which liked to go ker-snappity when you remove them. That (power?)stroke of engineering genius is, to the best of my knowledge, in the 2003-2006.5 5.4. I snapped 5 when changing mine, just make sure you have the extraction tool on hand before you start this project. If you're careful, you won't have to pull the head. I think the question I'd be asking myself is if I want a solid front axle or IFS. Which will work better for my application, etc.
Sometimes it is best to stick with the evil you know. I'd also try shopping around a bit, you should be able to find a 5.4 F-250 for way less than that!