Dude, that's like the "bank error in your favor" card from Monopoly. KEEP THEM, they are MUCH better than the stock E7 crap. You will need headers that fit P heads which the Ford Racing stainless ones do and the ones I recommend you get. If you are still having issues with the plug wires fitting you can get MSD universal boot ones (the ones where you bend the boots) or 90 degree ones.
2000 Mustang GT Steeda #0048
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.