The older (96 ond older) F-150's and Econoline vans with the 351 came with the E7 heads. I agree, they'd probably hurt performance. Going with an OEM head, get at least some GT40's from a Cobra, or the 5.0 Explorer before they put the "P" heads on, so you can use regular headers. I don't believe anyone makes a header for the 351 with "P" heads. Long tube swap headers may work though. Some do on the 94-95's without getting the swap headers.