In that case I imagine your heating problem is quite normal. Not saying it's ok, just that it would be normal for a datsun, especially with air-con (you will have the aircon radiator thing in front of you normal radiator meaning less cool air going onto you radiator).
A mechanical fan obviously pushes more air when the engine is revving higher. So if you are idling in traffic in Brisbane on a hot day, I would expect the engine to work up to those temps. If you put on an electric fan, it only kicks in when it gets to a certain temp and will keep working even in you are at a standstill. They don't seem to push as much air as the mechanical fan at speed (but generally the air moving through the engine bay at 60-100kph is enough).
I would either recommend a push/pull setup or at the minimum 2 pull fans with a decent shroud. I made up a metal bracket that bolts up to the radiator, you can see my thread here when I was looking into electric fans
http://www.viczcar.com/forum/index.php/topic,4003.msg34631.html#msg34631.
260coupe i think it was, said to just go with cheap ebay fans rather than the expensive (but good) davies craig type. Been on my car for about a year and no problem yet. If you have excess money I would say just go for Davies Craig, but yeah the cheap ones seem fine to me.
I'm not running a shroud at the moment and generally the temps are fine. I would like to add a shroud though so the fans don't have to work as hard/often. Just have to get around to fiber glassing one up.
I would still recommend that HPC on the exhaust manifold as well. Looks good and I think in your case you need to minimise as much heat as you can.
Just my 2 cents, I'm in no way an expert :S
