A tempting way to waste $300 and many hours of one's life.
The work done so far does not look terrible.
What concerns me is the room left for seats on this floorpan. The Miata tunnel width is like having a third passenger in the front row and this is going to require passengers to be slim and against the side of the car.
The seats in the Miata are never too far away from that rear bulkhead, and that rear bulkhead is not far in front of the rear wheel arch. So if we look at the profile, you might end up driving behind/beside the B post, while being crowded against it.
That said it has been done and works for some people. Here is one owner driving mostly in the back seat up against the side. My test metric is how well my elbow rest on the windowsill while cruising. So not ideal for me. Steering wheel needs to come off to crawl in the back.
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