the absolute best way to mount a seat in an s14 extremely low is this.
Remove stock seat. Remove cross bar going between the trans tunnel and the rocker panel, It has some spot welds just drill them out or air hammer them out. Once that is removed then cut out the hump in the floor board that is there for the factory catalytic converter. Then weld a new layer of floor even with the rest all the way to the tunnel. Then you can bottom mount a seat directly to the floor and it will be stupid low. Or then mount fixed side mount brackets directly to the floor.
This is what i will do with mine but i just don't have time before proam to get it done. So for now i ordered nams sliders from enjuku.