Great information there with one caveat. There are indeed different dimensions and offsets amongst the SOHC water pump pulleys. The six cylinder cars have a correspondingly wider bolt pattern on the pulley than the z-22 (don't know about the z24) but I purchased a pulley for a z-car and it didn't work - next I located an '84 Maxima with a 2.4 six which had a pulley identical to the z-car's so I didn't bother pulling it.
Now, honestly, I don't know what the heck the pump I have fits. Physically, it's identical to the one currently on the motor minus the fan clutch of course. I just went down to the local auto-zone and asked for a water pump for an '82 720 without a fan clutch. They had no less than four of the fan clutch type in stock and only one of the standard non-clutch type so, of course I buy that pup and head over to our local nissan only wrecking yard who promptly informs me that "No 720 ever came without a fanclutch waterpump, that's an aftermarket (?) pump but I may have something off of another application that might work" - hmmm, okay. --- So, I bought a pulley he had which was correct for the pump hub but the offset is such that it puts the belt on the innermost (closest to the block) groove on the harmonic balancer with no way to adjust the belt.
It was at this point that I decided to do some more on-line reasearch which led me to datzenmike and you folks here.
The board wont allow me to post pictures so here's a link depicting the pulley differences.
http://s71.photobucket.com/albums/i122/krautman1/Datsun%20720/
Doc