I have attached a link to some of photos of a '91 560SEL that was for sale on Bring-A-Trailer. Photo 114 & 115 show the mounting of the "Country" horns. Hope this helps.https://bringatrailer.com/listing/1991-mercedes-benz-560sel-6/

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1991 M-B 560SEL Arctic White/Grey 99,000 Miles
1987 M-B 300SDL Ivory/Palomino 229,000 Miles (sold but never forgotten)
2006 Volvo XC70 Blue/Beige
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1986 Porsche 928S Goldweiss/Brown