!
My car is a later car, so the rails unbolt with the seats. Early cars may have to remove the welded in rails, or possibly unbolt the stock rails from the seat and bolt them to the Miata seat? On the later cars, the seats bolt into SOME of the stock holes. You have to drill a couple of new holes. I had no choice but to swap the seats. The Miata inside rail is way to the side and interferes with the A/C lines.
There are two problems. The driver side inertia seatbelt reel is in the way. You have to move it up and re-drill a new hole (see previous posts for pictures). Easy.
Problem two is that the stock Miata seat PAN is designed to fit down into a depression in the stock floorboard. It has sort of a "butt-socket" to cushion your tailbone that hangs down lower than the rails. This has to be cut. It's easy, but you have to remove the stock upholstery and foam, then cut the center downward-facing hump out. This leaves a big square hole in the bottom of the seat pan. You also have to grind off the seat foam as well so it's all nice and flat on the bottom. Essentially you will be sitting on the floarboard of the car unless you weld in a piece of flat metal, but I didn't see any need.
Stock seatbelts on the Miata bolt to the seat, so I ditched those. More stuff getting in the way.
Honestly this is a very easy conversion, and the seats are much better. However, they don't create any additional legroom. In fact, the actually sit you up about 1/2 inch higher. But it seems that the seat back is thinner, so you can lean back just a bit more. Overall, it's not real noticeable.
And the seats are black, but they sort of reflected the camera flash and ended up looking bright gray!.