Had an early 260Z. serial number 002715, I believe. Most stable driving car I ever owned. Nose got light (well) over 100mph. Put headers and exhaust on it. Both helped. Take the rear drums off once a year to inspect and put back together with anti-seize paste (don't ask why I know). If you live in a snow area, figure on replacing outboard u-joints every year or two. I think I still have 2 of the old hubcaps in the garage and I sold the car in the early eighties.
Bilstein shocks helped the car too. This will start a fight: at 55 mph the car would get just barely 20 mpg. At 85 it got 26.5. Gearing was all wrong for that engine/rear gear combo. Those Hitachi SUs just did not run right at low RPM. I must have tried a dozen different plugs in the engine and different weight oil in the carbs. NGK BP5ES ran best as I recall.