I did my 01 v-10 2 years ago, and haven't had any problems, but I used bolts, and Ford headers. I can't recall what size the bolts were, but I think they were 8MM. I do know the bolts that came with the headers were too short. I read an article in a magazine about the 5.4 that said they got huge HP gains at the wheels when putting headers and a catback system on.