Rather than "piston" swap, I was talking about "piston engine" swap. There are Datsun 1200s with non-rotary Mazda engines in our Photo Album.

I doubt if anyone has bolted a Mazda engine to the 1200 gearbox. But you never know ... it is likely possible. In the old days we used to put Oldsmobile engines in front of Ford transmissions, etc. and racers are still bolting large Chrysler Hemis to small Chevrolet transmissions.