Well its about time!

I don't know anything about turbos, but I wouldn't get the ZXTuner tranny either. If you absolutely have to change anything just get a 4.06 final gear from the 99 S/R. Then like others have said, get strnger axles.

Every ZX2 made has the exact same final gear of 4.10:1.  The only difference in gearing is between the 98 model and all later models.  The 98 had shorter 2-3 or 3-4 gear sets.  I don't remember what two gears it was, but it was two gears.  The 98's tend to be a bit faster in the 1/4 and this is the reason why.

I am pretty sure but I thought the S/R, atleast the 99 had a 4.06 final. I thought it was capable of 156mph, it would not be able to do this with a 4.10 final on a 205/55/15 wheel/tire combo. Non S/R MTX ZX2 with a 4.10 final with the same wheel/tire combo will only do 144mph. Another reason to include the 155mph gauge and ZR tires. Of course that's only if you had the power to push it that fast.

I recently used the diff housing out of a S/R tranny in my 2000 case.  If the finals were different, it wouldn't work.  They are all the same, they all have the same code stamped on them to.  The S/R got the exact same motor and tranny as all the other ZX2's got.