I have a 1.9L Opel GT engine with a Weber carb that you can rebuild if you want to come over to WA... lol. Its super straight foreword and small, but parts are a BEEOTCH to find. I'd suggest a single cylinder Ninja 250 though. You can buy the whole bike for cheap, the engines have been around forever, and there are millions of them on the earth.
If you really want to do a car engine, the tried and true 350 would be a good start. Parts are everywhere.
ROTM June '13, PNW Crew #42, SR #245, Rally Rev #02