I'm using the tach from an '85 donor car so it shows accurate readings (see the thread about that install here http://www.peachparts.com/shopforum/diesel-discussion/390289-adding-late-model-w123-tachometer-3-pin-earlier-model-car.html)

I have the speedometer from the same '85 donor car available, would that speedometer be driven off of the same sensor that is driving the tach, or was the 85 speedometers driven by a cable?