A third option for you to consider would be a 3rd or 4th gen 3S-GTE engine from a Celica GT-4 or Turbo MR-2.
It's an inline 4, 2.0L Turbo, and puts out 230-265hp depending on the year and specs.
Here's a link to a video of on in a corolla, and many others on the side through youtube:
http://www.youtube.com/watch?v=srUcSXXzuHU
I know it's not a superbike it's reeling in or anything like that, but in its current state I don't think your corolla could keep up with a vespa.... lol
You can find them on e-bay for anywhere from $2000-$3500 for a decent one.