your speedo drive wont change (its part of your gearset), although you will probably need to change the sensor thats screwed into the speedo drive outside of the gearbox.

otherwise, all you need to change to 4.444 is to swap your crown/pinion on your main gearset (practically a complete gearbox rebuild), source a 1:1 centre diff housing (from any STI, JDM or non-turbo GC impreza). and a 4.444 rear diff.

your existing centre and rear diff centre are interchangeable.

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