Z33 seats have been done before (you can search on here, zilvia, google, etc) - there's a couple different write ups. You don't need to completely rebuild the seat rails, but if you are not comfortable with modifying & rewelding the brackets, I wouldn't suggest it.
S14 seats are your best bet - you can buy cloth ones & get them reupholstered; there are also stock s14 leather ones, but those are usually a little beat & overpriced.
If you are feeling really baller (and can let go of the leather part), you can get really nice S15 seats which bolt up to the vert also.
sci2000tech wrote:Another thing to take into concideration is safety. O.E.M. seats and rails are built to specific standards to meet safety requirements. Changing/replacing these parts will affect that.
I completely agree with this. I find it interesting that this is hardly (if ever) brought up when people suggest relocating the seat belts w/ the coupe/hatch door conversion.