Not really that much to it
https://forum.miata.net/vb/showthread.php?t=508247
On the NB, you need to fit the temperature into the filter by drilling a little hole. I woudn’t worry about finding the exact same K&N. I would also look at a Ram Air filter.
But on the NB, a cold side intake is where its at.
Gucci (Autoexe)
£20 version
Old thread