It is a botch up of a job .
Certainly , in the past , conversions of large saloons , Rolls-Royces even , have been used for this kind of work , even by major film studios ( look at 'behind the scenes' documentaries of even some of the early Bond movies for evidence of this - plenty of shots of a 'Silver Ghost' pick up truck) .
These cars are usually chosen for high mass and compliant suspension to provide a stable platform .
Unfortunately , as the previous poster has mentioned , this is a bodge job since the centre column is not level , which for any kind of cinematography is a no-no due to the camera going off level as soon as you pan in either direction . The issue of camera shake is another matter , particularly at longer focal lengths .
It would probably have been simpler/better to have sat an operator on the roof with a Steadicam , apart from being able to translate up/down with the crane .
As for the car - obviously it is a conversion since there were no factory W126 estates . Why they didn't pick a car with SLS since it was standard on the 560 and optional on the lesser models I don't know - an estate conversion pretty much requires SLS as a prerequisite . The 500 is , of course , a V8 .
Note in the pictures with the rig on the front of the car , it is nose down - so too much for the car's suspension .