I have this subject on Ford-Force and Viper replied....4th I'm not sure about, but on the MT75 the standard 5th gear is 0.83:1, and the Scorpio diesels and late (97,98) 2.3s had a 0.75:1 5th gear ratio which helps top speed and cruising revs. You'll need to dismantle the box totally, have the original gear taken off and the new one pressed on, then rebuilt. Only give it a go if you have the know-how!