Here is a link to an old thread that might offer some insight.
http://www.ford-trucks.com/forums/sh...latinum+anode+
The Motorcraft plugs I installed (as replacements) were all the same part number. That was about 50,000 miles ago and I have not noticed any change in performance, mpg, etc.
If you are about to change your plugs, I'd suggest a new set of Motorcraft wires too. Not very expensive.