A good swap would be the same motor that came out of it, because it's the only one that will really fit. If you wanna get into the race scene, become a regular here and read all you can. Also give
www.2gnt.com a look, they have an assortment of GREAT info in the tech section. My suggestion is find a used 420a motor, tear it apart, clean it up, and then build the shit out of it. Then you'll need a nice turbo and good fuel setup. That should get you some decent power.