There are a lot of motors you could fit in there, but why would you do that? I would put an engine in there. You will get a lot more out of it if you could run it without a cord.
You know, I think only like 10 people here will get that...
Obviously, least amount of effort and time, is a 22. but if you won't be happy with it, and you end up yanking it and doing a 3RZ in a year, then it costs twice as much and takes twice as long. Don't worry about how long it'll take(unless your other ride is a bus), and do what you want to it.