Is this an aftermarket tachometer? If so, is it suitable for diesel? Most tachometers use a coil signal for RPM's (something not available on diesels!). The BJ60's use a sender on the bellhousing to give a signal to the tachometer.
do you have a sender of some kind for your diesel? tachos use the pulses from the coil usually and divide by the number of cylinders to give the rpms. Sounds like kindof a lot of work to get one going. Tachos for petrols wont work.
aftermarket tachos for diesels are $1000+ with special fitment, if the engine didn't come with one from the factory.
Best way is to attach the tach to the alternator. Some alternators have a connector at the outside where A/C voltage is supplied. The frequency is relative to the enigine rpm's, though it is NOT equal because pully sizes are different. So you have to calibrate the tach, and for that you need an adjustable tach like http://www2.vdo.de/vdo/end_consumer/ec_product&fza=&ID=725.aspx (sorry, it's in german ???).
Most garages have the equipment for calibration.
If your alternator does not have the connector at the outside, you must disassemble the alternator to bring out a wire. More difficult though.
Where are you? I'm in Vancouver, B.C. and I have a spare bell housing from my BJ60 which has a space for the sensor to mount. You may need a different flywheel as well as I think is receives a signal from a magnet or something imbedded in the flywheel. If you're interested let me know.