Hi..can anyone tell me what header I have? 5/8" flange, approx 1-3/4 tubes, dual 2" outlet...thanks!

Datsun Comp header, it's in the " How to Modify your Datsun" book.

I don't have that book but, I've seen the picture in there of the "Cyclone" header...mine's not the same as that one...if that's what you're referring to. Is there another header in there besides that one that you're talking about?

You have the Datsun brand Comp header

This appears to be a Japanese market header...Datsun Spirit uses it on his 240Z and offers it as part of their exhaust system on datsunspirit.com. It is also discussed on hybridZ in the N/A 400hp Japanese L6 thread.

Nissan Japan 'Sports Option' exhaust manifold c.1971:

Thanks for sharing guys. Several of the parts I bought from this guy seem to be from the Japan only market.