Ok, those are sparco side mounts. They are NOT for using with Sparco slide rails, they are only for mounting the seat in a fixed position. The idea is to mount the adapters SO gave you to the stock bolt pattern, then mount the Sparco side mounts to them. Lastly, you slide the seat in between the Sparco side mounts and you're done.
I haven't used the side mounts, or snake oyl's plates, but I can tell you firsthand that getting everything in and mounted is a pain in the arse. The way I did mine was to use a set of brackets from Archer, which are shaped from a side profile sort of like a crowbar. They are designed to bolt to the floor, and have the seat bolt directly to them I think. First of all, all of the holes were off. I had to have a friend machine out the holes in order for me to do anything. I also used the Sparco sliders, which bolt to the bottom of the seat - but not without first buying some big flat washers to space the sliders off the seat bottom. Even the sparco crap i bought didn't work together. At least they wouldn't bolt to the bottom of the pro2000. So after a little ingenuity, I had the sliders mounted to the bottom of the seat.
Then it got real fun. I bolted the plates to the factory studs, then laid the seat in place and marked where the holes didn't line up. Then I took it all out and had the holes re-drilled. At this point I loosely bolted everything together to see if it all finally lined up. I put it in the car, adjusting it to fit correctly, then tried to tighten everything up as best I could. Then I pulled it out, tightened everything up firm (cause you can't reach much workin under a seat).
So finally, I ended up with a pro2000, bolted to Sparco sliders, bolted to the archer adapters. Now I can just swap it in and out in 5 minutes. The final kicker was that after I got it all in and shut the door - you find out the shoulder wings are really a good 1.5" too wide or so. So out came my dremel. You can disconnect the spring that holds the seat cover on and get enough slack to flip the cover off the shoulder wing. I then dremeled off the edge (this is all with the seat out of the car btw) and then put the cover back on and reconnected the spring/wire.
This is not a task for the meak, but when you're done, its awesome. I can take pictures of anything you want and post, just let me know.