You may have trouble finding a used set of 351 swap headers, but you can get some for a relatively low price. I think MAC makes some inexpensive ones, Ford Racing makes some pretty expensive ones, and there's a few other companies that offer them if you look around. I've found shorty 351 swap headers for around $200 in a Muscle Mustangs magazine, but i don't remember what brand. Do you already have the 351W swap oil pan and pickup tube for the oil pump? Good luck!
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'84 Mustang 5.0 LX
My car