The E3 plugs are a junk, snake oil product. Just like splitfires were. Are they even still around? Autolite 104s are $2 each and the stock equivalent plug. I run 103s as the modulars like running a little cooler.
If your COPs are in good shape but have not been done yet you can rebuild them. If they have cracked housings or are not OEM, best to replace them with new OEM.
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.