Im a welder fabricator by trade have been doing this for 11 years now, im coded for mig, tig an stick welding most of my skills have been used in my BMW project seen here http://www.mkivsupra.net/vbb/showthread.php?171394-Bought-myself-a-winter-project&highlight=winter+project
I have built several custom seat mounts for various cars including my old silver supra, the problem I can see with this is most of you will not have the same mounting brackets, I can make the rails like Jamie has an if you can let me know the pitch of the holes I can drill an tap them, i will keep all the measurements from the different subframes until eventually I should cover them all> As Nevins has stated above on my Supra I just made strut bars across the two rails and mounted the runners to these. I can make these to a high standard but polishing is not my game so more than happy for mitchell9006 to get involved an polish them or ill sub let it out to a company we use.
john