Erick,
I do have a MPH and KPH gauge for a 280SL (LHD) and both do have the connection for the cable on the right hand side, seen from the back of the speedometer. I have both gauges out of the car, if you like to see a picture I can take one. Both do have also the rubber jacket.
I do believe your connection on the left looks like for a right hand drive(RHD)car.
Lajos Damen
1969 280SL