the bride rails as far as i know they sit the lowest

The R039SO and R040SO bride rails do NOT come with the side mounts so keep that in mind (If your Sparco Evos are side mount)
(after seeing the link you gave it shows that the R039LF and R040LF type have the side mounts)

The mounting position on the side mount seats is roughly the same throughout the seats,
If the seat is narrower than the mounts (normally the case) there are "special" spacers to fill the gap

Double locking i assume your referring if the each rail "locks". Both bride and recaro lock on each size. I have both the bride and the recaro rails

 

^ Thanks so much for the help. I'm a newbie at this so the help is much appreciated.

I now know the Bride, Nagisa, and Memfab rails will work, it's just a matter of picking one and going with it. Am going to call the manufacturers today.

As for double locking, yes, sort of on each rail locking The Nagisa and memfab units in standard form only come with one rail that locks but you can order them in a double lock. Bride is double.

However, Sparco's double lock means they have two locks per rail for a total of four. This is the ultimate but they do not make them for the FD.

 

Yes the bride side mounts work on the Recaro as seen here
1993 FD3S Mazda RX-7 - Import Tuner Magazine