I've run stock Motorcraft, Splltfires, AC Rapidfires, and now E3 plugs, and they all fit properly. I like the E3 plugs over the others; better kick and tip in throttle response and come with lifetime guarantee. In my '89, the stock Motorcrafts do not seem to perform as good as the others. Did a back to back comparison of new Motorcraft (old style) vs
E3's, and did feel an improved kick with the E3's particularly when the secondaries opened.