One of the readers had an interest to get a time period correct radio installed. At first the Blaupunkt radio in my car was considered a good option (his car is from 77/78). But in the Original brochure a different brand is displayed. It was found out it's a Voxson. When doing further checking I noticed a lot of this had already been discussed on the FChat forum in this thread:
Still it's unknown what the exact model is. On the picture it's clearly visible and reads:
"quadraphonic stereo" I wasn't able to find anything more on the internet on this model. The normal "8 stereo Voxson" is well available and documented. Does anyone knows more about this model or has one for sale?
update 27-11-2015: Found it, it's a Voxson Quadrophonic Stereo Q8
More detail in this link: http://www.radiomuseum.org/r/voxson_quadrophonic_stereo_q8.html