a toprotege.com member has installed Sparco Torino seats and has provided detailed instructions (sorry, no pics).
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This is a step-by-step instructional of how to install after market seats using the stock rails and the universal slider found on most aftermarket seats. Some seats may vary but this instructional has a lot of flexibility in terms of design to accommodate many aftermarket seats.
Tools/Supplies you will need:
Steel L-Bracket 24'' per seat
Angle grinder or die grinder or ghetto file (will take longer)
Safety glasses
Drill
Slot head screw driver
Hardware to fasten seats to rails
Any sort of paint (recommend Tremclad brush on - mush thicker protection) and brush
Welder (if you don't have welder go to a ghetto auto shop and they will weld pieces for you - don't pay more than $30 for both rails)
Estimated Time for Install: two people - 8 hours (and that would be quick) Took me quite a lot more.
1. The stock seat must be removed from the car. Unbolt the four bolts that hold the rails to the floorboards. Then tilt the seat back and remove it laid side ways through the door opening (Wouldn't want to scratch the interior - also recommend you remove your door sill plates)
2. Now you must remove the stock rails from the bottom of the stock seats. Put the seat on the ground so that you have access to the rails. Slide the sliders all the way to the front. At the back of the slider base on the stock seat you will see two little bumps on each side. These bumps must be removed with the angle grinder. Grind the bumps flush to the slider base. Repeat on other side.
3. Remove the plastic plugs on the rail ends. You must now dislodge the roller bearing that sits between the rail and the slider on the stock seat. To do so use your slot head screwdriver and skillfully push the back roller bearing towards the back of the slider/rail. You can slip in the screwdriver through the slots in the stock rails. Once you are near the end work the rails/slider back and forth till you manage to get the bearing out from between the rails and slider. The bearing should fall out through the back. Repeat on other side. Note: This is a tedious step - have patience - don't get "spaztic", everything will be okay.
4. Now slide the sliders backwards and grind off the other set of bumps on the slider's front. Repeat on other side.
5. Grab the front of the rail's foot and yank fairly hard to slide off the rail from the slider bar. The rail should now be in your hand. Repeat on other side.
6. Get back in the car and bolt down the rails back into the floorboards. Measure the distance between the rails and cut the Steel L-brackets so that you can bolt them to the underside of the rails. On a P5 the length of each L-bracket should be 12''. Two L-brackets will be needed to mount the seat. One bracket for the front bolts of the seat and the second for the bolts at the back of the new seat.
7. Before you begin bolting double check the distance between your new seats bolt pattern. Space the L-Brackets accordingly and bolt everything up everything after drilling the necessary holes. Do the drilling and bolting outside the car so you don't mess you interior.
8. With the rails bolted up as tight as you can re-install the rails in the car to ensure nothing has twisted while you were bolting things up. Make the necessary adjustments.
9. Take the rails back out of the car and place it on a workhorse or workbench. Slide the new seats universal slider into a neutral position and place the seat on top of the rails. Mark where the holes need to be drilled in the L-brackets up front and in the back. In the P5 the new seat must be mounted approximately 3/4'' towards the inside of the car to ensure that your seat is centered in your steering wheel. Before drilling check for clearances if you were to mount the seat. Make sure the recline mechanism doesn't hit the center storage box or the center console. Also ensure that the seat is not being mounted on an angle (left/right). Note: On a Sparco Torino seat the recline knob must touch the center storage box for the seat to be centered.
10. Drill those holes that you marked after double-checking.
11. Fit the seat with the rails. Bolt everything together and go for your first test fit into the car. Again be sure not to scratch the interior when placing the seat back into your ride. Bolt the seat rails into the floorboards. If holes don't match up perfectly use a hammer to manhandle the rails a bit. Most a hammer will correct will be 1/4'' so if you are off by more than that think about where you went wrong and correct the mistake.
12. Get in the car and enjoy the new seat for the first time. Pretend you are a rally racing or dragster. Now shut up and stop gloating cause you're not done yet. Take a look at where you might be able to mount your seatbelt clip. (More on this later)
13. If everything is perfect you're good to go to the welder. If not make some adjustments but always make sure you test fit the seat to make sure you didn't screw up the geometry of the rails.
14. If everything is ready then remove the rails from the seat and head over to the welder. Get him to weld all the joints where the L Bracket meets the rails. If you need a welder who will do it for $30 I'll hook you up in a place in the WESTSIDE.
15. Once it's welded lightly sand the Steel L-Brackets and paint it with the Tremclad. This will prevent corrosion - duh and will also make it look sweeter.
16. While the paint is drying you can figure out where to mount the Seat belt clip. On the Sparco Torino there is a plastic cover that covers two bolts. I placed my seatbelt clip into one of the bolts. I found washers that were big enough to fit the bolt but small enough to pass through the seatbelt clip's hole. With this set up even if I tightened the bolt the clip would still swivel. This part will take some creativity. If your seats don't have this bolt you may consider building a custom bracket at the welder's shop to fit your car.
17. Once the paint is dry bolt everything up and down into the ride and you are good to go compliments of the WESTSIDE!!!
you can see it here: 
