As mentioned there are two different tach drive systems for the D1-30 engine
depending on its vintage.
Earlier engines (D1-30 A) pulled the tach drive signal from the Mitsubishi 115 amp alternator and fed this signal to the tach on the grey & grey/blk. wires. The tach is a 12 pole unit, and then you need to take the crankshaft to alternator pulley step-up ratio into consideration as well. This will then give you the pulses per crankshaft revolution.
Later generation engines (D1-30 B thru F) didn't use the alternator to drive the tach. A magnetic pickup mounted on the flywheel housing counts notches machined into the flywheel and feeds this info into the MDI box. The MDI box calculates the RPM
from these pulses and places the info on the CAN bus harness which is seen and displayed by the tach. There are no grey & grey/blk. wires on these models.
In any event, there will be way more than 2 or 4 pulses per crankshaft revolution.