As the rolling diameter of the wheel is similar to what other people are running I would doubt that you'ld have too many issues fitting them, as people have said you may have to roll the guards. If you can mock it up would be a good move.
I've read posts where people have said na6's on 16's handle like rubbish, are slow, don't do it, etc. And really in my opinion its not a huge difference as long as the wheels are still relitivly light, in my opinion you retain most of the handing brilliance of the car, just loosing a bit of feedback and response. 19's on the other hand may not be quite so good in this regard, but as handling its not your reason for having the car, why worry.
If they fit and you can put up with the ride quality and the handling aspects of them. The only issue I see is the legality, I thought you weren't meant to go up more than 2', although I may be wrong. I look forward to seeing what they look like, love it or loath them, it'll definetly be different..
Although I disagree and think that the mx5 looks fantastic, on 14's or otherwise.
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