If you are just looking for replacement non performance rebuild stuff, I ordered pistons and a timing kit from here: http://www.store.partsdinosaur.com/page278.html It got to me very timely and the guy was awesome to order from. The piston brand was "Safety Pistons" and there wasn't anything wrong with them as far as I could tell and the machine shop didn't mention any issues when I had them pressed onto and balanced with my stock rods.
I got my Clevite bearings from www.rockauto.com and I ordered my Clevite/Perfect Circle rings on ebay. The only real performance stuff I bought for my rebuild was ARP head studs and rod bolts which I bought from Summit. I went with LD28 Maxima Diesel main cap bolts instead of the ARP due to cost and got those from courtesy parts. The diesel bolts are stronger and take about 20 lb/ft more torque than the regular L28 main bolts.
You should definitely have your head at least milled to a gasket surface and have it checked for any problems, that cost me about $80 at my local machine shop. My cylinders were in good shape and within spec so instead of reboring them I bought myself a Flexhone tool for about $50 and just honed them myself.
I highly recommend downloading the Nissan Factory Service Manual for the 280ZX Turbo and also get the books How to rebuild your L-series engine, looks like it might be out of print but if you search around I'm sure you can find a place that has it in stock: http://www.amazon.com/Rebuild-Your-Nissan-Datsun-Engine/dp/1931128030/ref=sr_1_1?ie=UTF8&s=books&qid=1253291889&sr=8-1
There is also the How to Modify your Nissan/Datsun engine book which is good: http://www.amazon.com/Modify-Your-Nissan-Datsun-Engine/dp/1931128049/ref=sr_1_3?ie=UTF8&s=books&qid=1253291953&sr=8-3