What's the proper "stance"? It's all subjective. Lowered cars rarely pay dividends on the street outside of crushed air dams and high-centered speed bumps. The 260 and 280Z have a higher stock ride height than the 240z, but lowering it an inch or two will produce the appearance of the earlier car. As for wheels and tires, a 225 50R15 on a 7" zero offset wheel seems to work nicely on a slightly lowered 280Z.