Rich, I have a 1984 Euro 500Sl. I am pretty sure it has the electrontic speedometer. Have you traced the cable back to the transmission? Do you have oversized rims and tires on your car? Perhaps that is why your speed is different. Lee, I have the small bumpers. As soon as this weather breaks( sleet and cold as heck) I'll take off the car cover and try and get some pics for you.
Mike
1985 380SE
1984 Euro 500SL