Its a bit of a fiddle. I think one of the main things i hadnt really considered is the exhaust needs modifying to clear the diff properly.
We heated mine red hot, then with a suitable die squashed it in a large press to ovalise the pipe. Worked a treat to.

Don't cut any corners. If your using a fitting kit get a MT rear cover to ensure nothing breaks. I've found motul 75/90 ls300 diff oil pretty good and I've tried a couple now.

It has changed the handling characteristic of the car a little. Bit less stability on the rear when pushing on. Could just be my diff though. Got mine off ebay and it could possibly do with a refresh at some point.

What ratio is yours? As others have found previously the 3.9 is a real sweet spot for fast road.