What's the factory redline on a 260Z?

On a 240Z a junkyard stock motor will run 7000 all day long. With forged pistons we went to 7400 when necessary. The weak link is the ring lands on the stock pistons, but the mode of failure is usually just wear leading to higher leakdowns.

To have that much damage sounds a lot like detonation or seriously overlean on one carb. For a long period of time. Rather hard to destroy an L series motor in IT trim. Sorry to hear about that.