You will need the two metal pieces that go underneath the tail lights. The piece you are buying takes place of your whole centre piece with no issues. Same dimensions. Also, what are you doing with your Euro MKII tail light centre piece by chance?
I know you posted before, but look at my post and the two pictures of the rear of the black car. That will show you the difference between US MKII and UK MKII.
You have

What it will look like and notice the two metal pieces below the tail lights (has he Silvia decal on the left one and a dragon on the right one)

or
http://www.nissansilvia.co.uk/vbb/showthread.php?t=4910
Just a note, your number plate wont fit into how short ours is unless it is modified or you get one made up.