It's a Euro Spec widebody in the USA, which means it's very rare. The Americans place a premium on these cars as they were so much more powerful and better looking than their own...
It's why so many of the parts I sell ship to the USA, there's quite a lot of excitement about this one in particular on Benzworld.
It does appear to be a genuine "factory" conversion, as genuine as an after market factory conversion can be.
I just happen to think they are very undervalued here in the UK at the moment which is why I buy any interesting bits I come across.