mysterious spark plugs

89 bronco 5.0...............


so i went to change plugs this morning, i pulled out the first plug motorcraft p/n awsf 44p, took one of the plugs i just got at orilleys, motorcraft p/n asf 42c. i new they were different but i figured the p/n had changed sometime in the past. wouldnt you know it, the thing doesnt fit. so i call back up there to verify that the guy who sold them to me wasnt high, and the p/n was correct, so went to auto zone and got an auto lite plug p/n app 25, the replacement for the plug that i pulled out of the truck, same thing just doesnt fit. has anybody ever gone through this little scenario? the sticker on the air box says i need the motorcraft p/n asf 42c, but i doesnt fit. somebody please let me know what the hell is going on, was this motor switched to some other ford block?