That is the spec r trunk brace. I have it on my S14 as well as the two pieces in the front of the trunk. The spec r also comes with B pillar bracing that attaches to the floor and C pillar braces that you can just make out in one of the pics. The spec r also had roof reinforcements and front and rear underbody reinforcements that tie the frame rails together.
Apart from the roof bracing I have all the parts. The frame rail reinforcements made a huge difference! the rest, I really cant say.
