What I can remember from my old days (LOL) and from waht has been done here, you keep your original rails on the bottom. Then either take the sliding rails from your seats or get some from junkyard, fab up the necessary harness in metal and weld it in there (like under the svt seat) or bold it in with sturdy bolds. If all done right you have now the sliding parts under the seat and those will fit the rails in the bottom.
ZETEC CREW # 121
Volant intake, RS headlight kit, motor/interior parts painted
2'5 Header, flex & exhaust, Saleen/Eibach susp. & swaybars, small turbo to get some more oumph