Do you think it would be possible to swap Suzuki Swift GT engine into Justy?

 

Suzuki Specs Link

Different engine - doubtfull without heavy modifications.

 

Suzuki's and Geo's have little in common with the Justy, other than being 3 cylinder econemy cars

 

GD

It would be more productive and not too far fetched to swap in a street bike engine and tranny. Mount it at an offset with the tranny output shaft driving the input of a LSD diff. Gear it for a bit higher than the intended gearing so that instead of a top speed in the 160 range you shoot for 120s. That will compensate for the extra weight of the car. Not too difficult to end up with 140Hp and a 6spd tranny.