Dane
the zd30 uses a crank angel sensor which relays info back to your ecu then the ecu sends a signal to the intrument cluster which gives you your rev tacho the sensor is located at the front of your engine above your lower pulley.
td 42s uses a diffrent style of cranks sensor which looks diffrent and reads from a diffrent location.
im not to good with the td42 but some of the guys on here have done the swap before and they would be abel to help you out better then me