FD RX7 seats into Miata
 

Let me start off with:
If you are 6' or more, you may want to seek other seats. I am 5'10" and there is not much comfort outside of my normal seat settings. Not to say you cant make them work, but giraffes have been warned.

edit: the bottom section of the seat matches miatas fairly well, foamectomy may be an option for tallfolk.
https://cimg2.ibsrv.net/gimg/www.mia...400227aba9.jpg
Seatbelt tower makes serious contact, inhibiting reclining with not much forward space to compromise with. Rubbing noises accompany.

Onward,
​​​My back does not agree with NA seats on long (1-2h) drives, with NB 1 and 2 seats not being much better. "Surfboards" is an apt name. I elected to build this car around cruising so i had to do something...https://cimg6.ibsrv.net/gimg/www.mia...77056f927d.jpg
A cheap set of FD seats popped up locally and after sitting in them once i loved them.
FD seats are a bit firmer with actual bolstering and look way better while still looking factory. They seem to fit the contour of my back better instead of being a rigid wall to rest against and i can sink forward a bit despite a lack of recline. They feel lighter but its hardly noticable with the rails on. I would love to try FC seats someday as they are more couch-like and nearly incited me to trade platforms.
The best info i could find on mounting is from mnet '07 wherein OP heavily modified the FD rails to fit and stressed how difficult adapting them was.
https://cimg4.ibsrv.net/gimg/www.mia...3bc9ada675.jpg
Despite only having Miata rails to play with, I had almost no issues between how i thought it would go and how it went:

Miata rails are noticeably shorter but bolt to the seats in the same manner, bolt size and all. The FD's mounting holes are also further apart. Each corner gets a 2.5" coupon with holes drilled about 1.5" apart (with massaging) Use pythagorean therom, a tape measure and some m8 studs here.
I replaced the aluminum scraps with 1/4" flat stock and intend to weld them to the rails because why not make it permenant?
https://cimg2.ibsrv.net/gimg/www.mia...ce79763451.jpg
Scrapping it together first makes it seem too eazy to stop
https://cimg5.ibsrv.net/gimg/www.mia...b25dd5f33b.jpg
My adjustment wire broke but needed replacing anyways as it is not long enough. 3/16" stainless tig filler was perfect and wont rust to death like their predecessors.
https://cimg5.ibsrv.net/gimg/www.mia...c224cc250d.jpg
A little wiggling, prying and pushing and they pop right in like factory. New covers and some fresh foam are an obvious wintertime project for the driver's seat.
edit: i skipped this step and bought some in decent ~jdm suede~

as long as you respect the bolt pattern between the factory miata seat mounts (seat to rails) and find some way to attach it to the seat it just sorta works. Bonus points for being able to thread the bolts by hand without budging the seat on the first try.

Forgot to finish here. My spinal column and I are quite happy with these seats.
Added an extra stack of stock so it didnt drag on the carpet so much.
Thurough cleaning, painting and greasing. Both seats go in and out like factory with all plastics on, the seat belt loop is picky about how it returns but sorta works, maybe its just lazy after 30sum years.
https://cimg0.ibsrv.net/gimg/www.mia...4bb37c6928.jpg
Im in the midst of adapting S2000 seats next, however they are folds more intricate to fit and work than FD seats.