One thing that @Longitudinal mentioned when comparing potential candidates for a swap is the torque (vs HP). I am a big believer in a high torque engine for a street car. And I should clarify that all of my comments regarding swaps are referring to a street car, not a race car (I'm not sure what classes you could even race a engine swapped car in, other than one of the comical events like Lemons). The power curve for any engine being considered should be a decision factor. That's one thing I like about adding a small turbo to most engines, it bumps up the torque a lot (I mean "small" in regards to quick spooling). So a swap candidate that may not have the top power figures, but is a good easy turbo build, would factor high for me (and by "easy" I also mean affordable).