Re: Imho...
Greddy/Trust made the best header for the Z, copied by OS, or vice-versa. Neither are available here in the usa. Fitment requires nothing special, no special gasket, no leaks nuthin'. Last forever without rust through, and have a fully integrated exhaust designed after the factory Nissan 432 system, fits the 240 wonderfully.
Fujitsbo also makes some great headers, some of which will not fit on LHD vehicles, but that's another story...
Anything short of the old NISMO header available in the US has been a gob-job conglomeration of thin tubes that rust through, and cheap flanges with washers welded on to make them fit with the stock intake manifold. IMHO, all the US built stuff is crap. Until you see one of the Japanese headers, you don't know what yu're missing.