Yes, I installed a Sparco adjustable (vs fixed) back seat about a year ago now. I got it off of CL here in Seattle for $350. The stock slider just unbolts off of the bottom of the volvo seat. I fabricated some adaptors to mount the seat. I then used two peices of aluminum flatstock that I had lying around (steel would work fine as well). I drilled holes that matched the slider mount and some more that matched the seat. Bolted everything together (with the suitable amount of cursing of course) and it worked fine. I had the Sparco slider as well. I just used the Volovo one since I figured it would be easier to modify the seat to slider position than the slider to car position. The stock slider has a strange mount on the bottom with a couple of tabs on the back and some clips and stuff. Looked like a big PITA to futz with.
