Putting other motors in the 360 is a challenge because of how little space there is to fit one.
I know that somebody in Japan had fitted a 200+hp Mazda RX7 engine into one, and I know somebody had also fitted a BMC Mini engine into a 360 van. But both projects are pretty complicated swaps, requiring total replacement of all of the 360's drivetrain.
A imple way to gain power is replacing the top end of the engine with parts from a Subaru R-2 this boosts power from 25 to 30hp. But good luck getting someone in Japan to send you the parts.