Hello Matt, the Porsche horn is the correct voltage and frequency, so there's no reason it won't work on your car
Have you seen a picture of the connections and bracket on the back of the horn, do they look similar to those of the original Mecedes horns? there are plenty of pictures on here, if you search "horn" or "horn bracket" using the search function above left
I think the brackets varied between the years and whether the car had AC or not, have a look at the pictures, they should help