there's an easy way to work out the ratios if you have the box, you'll need one hand, at least one eye, some sort of marker like a twink pen, and the ability to count to at least 4
You can get a better idea of gear ratios if you take off the end cover of the gearbox (where 5th year lives) so you can count rotations of the input and output shafts.
If it's anything like the ST165, ST185 and ST205 boxes, the front diff is a 1:1 ratio, so comparing rotation of the output shaft of the gearbox to rotation of the front driveshafts will give you the centre diff (final drive) ratio.
On the GT-Four boxes, from the centre diff you actually have a torque reduction (i.e. speed increase or what would be considered a gear ratio of less than 1), which is the exact opposite of the rear diff ratio - this means that from your centre diff to your rear diff the effective ratio is still 1:1 to match the front diff. In other words, from centre diff you have a ~2.9:1 ratio, then the prop-shaft to the rear wheels, then the rear diff is ~1:2.9. So, to make sure it's compatible with your rear diff, you want to make sure the ratio of the front driveshaft rotation to rear prop-shaft rotation is the same between your old and new boxes (lock the gearbox so it doesn't turn when checking this)
I'm sure that's all clear as mud
