The rear has to be the same ratio as the front diff, auto or manual.
Depending on which box you are putting in the car. If you use a box with a different front ratio, you will have to get the rear diff from the same car as the box so that you have the same ratios.
To use the 4.44, 4.1, or the 3.5, ratio you will have to swap the ring and pinion gears, from the low ratio diff and fit them into the SVX housing, using the SVX Limited slip centre, so that the SVX axles will fit the diff, they won’t fit the low ratio diff from another model.
If you use a 6 speed that box has a front ratio 3.7 the same as the rear diff in your VTD and you can still use the R160, changing to the R180 is not necessary.
