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I have the Thorleys on my 6.8l SD and they are great headers and produce lots of torque.
I think Summits website is wrong. The headers they list are for the 150 5.4l as I don't think Thorley makes headers for 99'-04' 5.4l SDs just the 6.8l. If your interested in Thorleys I would call Thorley direct to make shure they have headers for your SD.
Got this off Thorley's site. (217 Part#) THY-217-C
CERAMIC COATING, 1997-2003 TRUCK EXPEDITION, 5.4L, 2/4WD, NO SUPER-DUTY, WITH FEMALE EGR FITTING
List Price: $858.00
Yes, you have to watch the application guide on the Summit Racing website. If you click the installation guide (pdf.file) for the listed Thorley header, it clearly states that the header is the for an F-150. However, I think that Summit Racing either infers or has customer feedback to recommend that a part will fit additional applications. I completely agree with dkf that you should contact Thorley for fitment verification before you make any purchase.
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