|and I was looking for a 'bolt-in' solution. Much of that inquiry is directly transferable to the R230 and TT subframe data; however, there are undoubtedly other combos available for the TT owner who wishes to change gear ratios without major fabrication.
Also important is learning the differences between diff cases and rear mounting one or two bolts (concentric bushings are available to match some bolt patterns to differing bolt patterned cases). Finally, there is the ubiquitous 'long nose' vs 'short nose' carrier housings. While the rear bolt patterns have a 'clean' solution, remedies to adapt the pinion length housings vary from what looks like medieval iron age butchery to some pretty sophisticated machine work.
I initially looked at using some of the welded plate fabrication designs that will swap long nose housings into short nose subframe cradles (NA and TT); but finally decided the cleanest approach would be to use an early 90's Q45 unit, rebuild it, and simply bolt it up to the NA chassis. This was accomplished by swapping the six bolt axle flanges with five bolt ones. Then everything dropped into place without anything more than changing NA flange bolts from 10mm to 12mm.
If you've got the money, Whitehead Performance in Ontario CN is the go-to-source for these adaptations. They regularly import JDM units and for these swap applications.