Monteverdi Sierra intererior seats

One of the things we have not solved is the mystery of the used chairs in the Sierra.

According to the German Wikipedia they are coming from a BMW:

https://de.wikipedia.org/wiki/Monteverdi_Sierra

"Im Innenraum installierte Monteverdi Sitze von BMW, die ebenso wie die Seitenverkleidungen mit Leder bezogen waren"

It was unclear exactly which BMW model was used. So I posted the question on the Monteverdi Facebookgroup. The first response was a 7 Series E23. This was potential a good guess, the E23 was launched in 1977 around spring. So actually to new to be used for the Sierra which got launched around the same time. Also some other details were slightly different. The next post mentioned the BMW 5 Series E12. Another good guess and a car that started production in 1972. But again some minor details were different. Then someone mentioned the BMW E3 with the electric adjustment used from the Aspen. The E3 makes more sense production wise but also the details looks correct. And he was right about the reused adjustments from the Aspen:

Note the power controlled seats (and windows) were optional and only for the driver seat

Find all Dodge brochures here: http://www.lov2xlr8.no/dodge.html

And for comparisson the Aspen chairs and the used E3 chair. In fact they had quite a variety of chairs in the Aspen, pending the model used and how luxurious you wanted it to be:

BMW E3 seats:

I'm unsure about the rear bench used though in the MV Sierra, I suspect it's Original whereby they added headrests and an armrest to it. Likely the headrests and armrest are coming from the E3 as well.