Because of the different years and engines, there were four different harmonic balancers used on the Z31's VG30 engines. Below is a chart to help determine which one you want to use.
|Year||Engine||Aspiration||Part Number||PS Pulley||AC Pulley||H2O/Alt Pulley|
You can use the A/B series balancers on the W series crankshafts if you get the spacer from Nissan (p/n 12308-V5321).
You should be able to use a W series balancer on an A/B series crankshaft if you get a slightly longer bolt with matching threads.