I live in California and failed the visual inspection part of the smog because the technician couldn't find the C.A.R.B. oe number for my headers. Did they even have CARB numbers back in the 70s? (1976 280z).

Mine headers are stock but he still asked me for it. That's what I'm asking.

Nissan didn't use tube "headers" on these cars, they all came with cast iron manifolds.

I'm still puzzled about why he said I needed the EO number to pass when everything is stock...

The tubular header is not stock. There have never been any smog legal headers made for the Datsun S30. The market is too small to go through the expense of getting a EO sticker. You will ahve to remove the header and replace it with the stock exhaust manifold to pass smog.