Since you have the shell & want a motor/trans for boost. I was just reading 1 of my import mags Super Street to be exact. Its a guy w/ a 03 S2K with a SR20 making 425 hp/385 . It's nice. The mag is April 2010. Since you want boost I feel thats a great motor/trans since its already turbo. I personally would get another F20 & boost that. It's all Honda. The S2k should stay NA just like the ITR/CTR. To each its own..

Good Luck & post pics