For Sale:
One pair of side mount race seat brackets for an NA (and maybe NB?) Miata.
These are not an off the shelf item. I got them from a fabrication shop a couple of years ago, but I never used them. I believe that they were cut on a water jet machine and bent on a brake. They are designed to use the factory front mounting points and mount to the floor at the rear. Ideally, you would remove the rear seat mounts from the floor. The seat mounting holes allow for a crapton of seat adjustment options, especially if you are using an aluminum seat. You can fit up to a 16 inch wide seat between the mounts without modifying the transmission tunnel and probably a wider seat with some messaging with a BFH.
$100 plus shipping.