Motorcraft parts are all sourced. So at any given time, they may come from a manufacturer that produces another line.
Motorcraft and Autolite are not the same product. Though Ford did own Autolite at one time, they don't now.
If you purchase an Autolite plug and compare it to a Motorcraft plug, they will not be the same.
Even if a product for....say.....Autozone, comes from the same plant as for NAPA, that doesn't mean they are the same quality. Each seller will have specific request for their product. In my example of parts stores, Autozone sells "discounted parts" (from their own signage.). They sell at a lower price because the product cost less to make than that of NAPA's. Which means there is a quality difference.
For my 1994 4.0 and probably my 2005 4.0, Ford used to sell a different set of plugs depending on what bank it was for. The difference? Is that the waste spark bank had the platinum on the ground electrode and the positive fire side had the platinum on the center electrode. (Reversed? Don't know but you get the point.)
Going to a parts store and getting the Autolites, you either get a single or double platinum, but you won't find an Autolite with only a ground electrode platinum.
Sorry, not meant to be a rant.
Edit: always willing to stand corrected. Just don't ask me to smile about it.
