"Thinking of changing the seats in my +2s 130/5, and have been offered a pair of Mazda MX-5 seats. Is this a straight forward swop?"
I have recently done this, albeit replacing my worn XJS seats that had, in turn, replaced my originals. So a lot of the tweaking to install had already been done.
There is a lot of info on the various ways to fit the newer seats above and on the forum.
Seats are VERY comfortable, but firm. I was worried that they may prove fatiguing after a while, but did a 600 mile round trip in the summer over a few days of mixed driving and was surprisingly fresh getting out of the car.
My 2c is that the MX5 seats raise you quite a lot in the car. My head now touches the ceiling in the car, driving position is less 'Elan sporty' and line of sight is slightly obstructed at top of screen. (I'm 185cm tall, so not overly tall).
I will probably need, at some stage, to remove some seat padding as the runners are as flat as possible.
See this post on a TR forum:
http://www.74tr6.com/miataseats.htmSeats do look 'right' though.
Best of luck,
Peter