How can you tell if EQ Heads are from New Zealand Foundry

That was comparing head flow years apart with likely different atmospheric conditions and probably different flow benches, and they only reported 4% difference. That’s like 9 cfm under those different test conditions for a magazine article. It basically tells us any of the old castings are probably equally good.
The currently available EQ head, as of the end of 2020, and all other cast iron copies are the ones to avoid when trying to build higher power, so just leave those for lower power or stock builds, like trucks.