Here's a little help, Ive bolted my rear evo seats where your back goes but haven't tackled where your butt goes yet...
FROM vr4460mez
Trim the foam, bend the support bars in the seat just enough don't cut them, and drill out the welds on the two brackets were the factory seats would latch onto and remove them. Then either use a screw or weld on a nut so you can use the hooks on the evo seat to bolt the rear seat down and pushing it back to close up the gap at the rear. The nut or screw would be attaching the evo seat hooks to the metal brace running across the bottom of the seat. It's kind of hard to explain without showing you mine. If you have more questions let me know.