Girlfriends cavilier, what should I do with it?

[Amphiron]

My girlfriends 2000 Cavilier just went down. It's blown a headgasket and its had a rod knock forever. Shes getting a new car and the Cavilier seems like something id like to play with? I might just give her $300 for it to put towards a Lancer.
My goal here? A junkyard built autocross/back up car I can drive when my stealth is getting work done.
I plan on tearing everything out of the car that is unneeded and making it light as possible after that I wanna do a engine swap. I don't know if anything is going to bolt in there directly that has more power, but that would be nice. I know a 4g63 wont bolt in there so thats out of the question... Any suggestion?