Carat Duchatelet is a model built by a "coachbuilder" in france i think. they fit all sorts of things to the W126 like rear seat tables etc,.. they are too tacky in my mind and shoudl be steered clear of.
As far as i can see that kit is a Lorinser kit for the W126 but sadly in the 80's so many people copied hte Ferrari testarossa that it's hard to be 100% sure. Even AMG ofered a widebody kit very similar to this one. it's not advisable to do this sort of conversion to your car as it'll kill all value that it has, specially when you consider the condition your car is in. If you really want to go widebody you'd be better off getting a denter to do the conversion in PK and getting the bumpers altered by a specialist (yes it can all be done here)
I'm familiar wth your uncles car, the rims on them are lorinsers which look alot like the SLR rims.
here's the S50KS8 by kleeman,.. the kit your uncle is getting should be like this one:
