What a beast, looks similar to the Toyota Crown Coupe's of the same era. As for wheels. Datsun's don't like the super low offsets that Toyota's will accept under the factory guards (as a general rule.) I've got some 15x7 +20's on my 180b and they're a perfect fit, yet get 15x8 +0's on my Celica TA22.
You do have a few options though as there are a number of quality wheel manufactures in Australia. CSA / ROH / Whitehorse industries are the 3 big ones that spring to mind. Now CSA use to make the Cheviot wheels (think globes / hotwires / jellybean) wheels you seen on heaps of old school cars (including my Datsun.) they may still be able to cast new ones for you. Now ROH make a 3 piece wheel called the
FLOW FORMED SERIES - VENTURO, which is available in any size/offset/PCD combination you can think of. that's definitely an option. Whitehorse industries bought all of the Simmions kit when they went belly up so they can make anything you want as well (but more pricy.)
Cooler option: Now what a really Kool Kat would do it get hold of ROH or CSA and inquire about producing a set of pressed steel wheels in the width you want, and then run the stock hub caps (which it looks like you've got,) with a set of either stretched 13" street rubber (can't seem to find much wider than 185, or a set of
Avon ACB10 Semislicks. which are available in up to a 245/45R13 and are of course street legal.
I take it this car wont be a daily more of a weekend cruiser. Keep the stock hubbies they're part of the history of this ride and you've got them. We're fortunate in Oz that we can get all sorts of wheels made at good prices, lots of people just don't know where to look.
Regards
Jordan