Uhh...Neil.....
I have referred to it as the "Q45" diff, not the R230 (at least since this debate started)......I'm sorry that you are so easily frustrated....
If you haven't yet, join the MS BB group here:
http://www.msefi.com/index.php?sid=85fe0503383c0ed4166671151442b54c
There are some really brainy dudes there!!
Could also very well be a 'donated' vehicle. Many people donate them to a charity 'clearing' house, they go to auction, if they don't sell, they go to the yards......or the JYs buy them at auction for rock bottom prices.....
To the best of my knowledge it is impossible as the engines were never CARB, or Federally approved or sanctioned. Without that as a starting point, I can't see that it is at all possible to have it certified. Maybe if they are somehow certified through Motorex or some other import house? I dunno.....
I believe that 91 through 97 are all the same. In 98 the bolting system changed from using tapped threads in the diff flanges to using nuts and bolts to bolt up the CVs to the diff.....