I had a Corbeau tube-frame racing seat (FX1 maybe?) in my RallyCross B13. Built a simple frame out of 1-1/2"x3/16" steel that bolted to the stock mounting points, bolted a Summit Racing slider to the top of that and then had a couple more pieces of steel to adapt the slider to the seat. Not only did it hold me in place while competing, but I actually did a couple of 200+ mile trips with it, and it was way more comfortable than the stock seats. I fabbed a bracket that held the stock seatbelt latch from the stock seat too, so I could cruise with the stock belts and not have to wear the 5-points all the time.
In my B13 rally car, I've got Sparco Evo series seats, which will be mounted using the Sparco side-mount brackets, and tubes run from the door sill to the tunnel. No sliders, but the Sparco brackets allow the seats to be adjusted if necessary.
I have in my shed, a pair of B13 seats that were done up in charcoal grey leather. Fair condition, not perfect. In fact I have an entire leather interior for a 2-door B13. Probably will sell that at some point.
A word about the Corbeau adapter brackets they make to fit specific cars. They're crap. there was one on my Corbeau seat when I got it, and it had been bent all to hell just from the previous owner getting in and out. I was just as glad I wasn't planning on using it (it was for a GM/GC Subaru 2.5RS).