The rods you are looking for are out of a '73 240Z. They're a little bit tricky to find since they were only made for one year (they may have also been in the early 260Zs). I'm looking at buying a '73 parts car this week just to get the rods.
About the Z31 setup, there's a sticky in the turbo section that will probably answer alot of your questions.
I agree that the L28et bottom ends are really tough. I may go with forged pistons on my next build but it's mainly because I want to raise the compression ratio a little.