For 750 & some early transition 750/101 series Spiders with adjustable driver seat and fixed (non adjustable) passenger seat. The floor rails are max. length 450mm, supplied complete with rails, seat adjuster stops, catch & knob for the driver's seat. True 750 series Spiders have a fixed passenger seat, although 750 to 101 series transition or "interim" Spiders may have both the seats adjustable on rails. This is not particularly well documented in the factory Parts Books. That's all part of the wonder of Giuliettas.
 
Part Name: Spider Seat Rails (Tracks) Set, Left, For 750 Series Driver
Alfastop Product Code: 1CWF226
Original Alfa Romeo Part No: 1495.68.704 & 1495.68.705
Model: Giulietta 750 & 101
Quantity Per Car: 1