Yet Another Tach Question
 

I have concluded, possibly inaccurately, that the tach used on a 300D Turbo is electronic. Therefore, the infamous tach-amp, that never seems to work properly, takes the place of the signal generated from the distributor to the electronic-ignition box of a gasoline engine. The question then is: Would a tach from a 300D (5 cylinder) work on a 6 cylinder gasoline engine if wired to the distributor-to-electronic-ignition box?

If it did it would be off due to the number of cylinders

The tach amp gets it's signal from a sensor mounted near the front of the crankshaft. All you need to do on ANY engine you choose to install in your 300d is to install the sensor on the new engine and also install a single trigger for it on the crankshaft pulley or harmonic balancer. I did this on the 4.3L V6 I installed in my '82 300D Turbo 123. It has worked real well for 4 or 5 years now. I did have to resolder all the connections on the tach amplifier board, which is mounted inside the cap that screws onto the connector on the drivers side inner fender to get the tach amp working reliably, though. (A common problem with all the lead-free soldered connections in our Benz's.)