well... what kinda experience do you have? do you have anyone to help you out if you f#ck up big time?
i would say just about any resonably sized north-south 4 cylinder would be easy to fit, consdering that you dont rush at it hammer and tong
i'd have to say something like a 4A-GE or 18R-GU, or rebuild the K engine with stronger internals and a turbo the size of a small country hanging off the side, ultimately its up to the way you drive and your mechanical knowledge to which engine will be best...
you have to also consider, can you fix the engine going into the car?? one of my mates did the 13B swap into something like a KE30 and everytime he needed repairs he'd have to take it to a mechanic