from the outside diffs look 100% same, only drive shaft flange diameter is different, there are 3 different sizes, but the problem is that you have to know exactly what you are looking for, there are 3 letter codes on casting from the outside and those codes give you all the info you need, but you also need documents to read first.
yes VAG tells us that the unit is sealed for life and major parts are not available only seals and axle shafts and few other things, i have so far opened up 2 diffs with 4.1 and 4.55 gear ratios and everything inside was interchangeable, ring and pinion, axles....
you mentioned that you need more proof...... im sorry mate i dont really like grumbling, but i have bought the diff only for this purpose to get this measurements, i have spent my own money and i have spent lot of my time to get at this point with help of many other clever forum members with documents and many other stuff i need to know so i could speak to ARB or Harrop or any other company and literally begging them to make diff lock for Touareg and cayenne,
and now you need more proof... sorry mate i dont have sponsor to buy all versions of diffs only to proof you that they are all the same inside and you can swap anything that you want, i already did my research that satisfies me and gives me confidence that i can go with this, so if you need more proof do your own research mate