Hello. Welcome to FixYa. I am Toyota Ed; I will be assisting you today.
The differences 'side by side' are negligible. The main difference, one that you really cannot determine by the eye, is the size of the combustion chamber. On a supercharged Previa, the compression ratio is markedly lower, because of the supercharged air being sent into the engine. The combustion chamber on a supercharged engine is slightly larger, and the piston domes are shorter.
Note: All turbo and S/C engines have lower compression ratios than a normally asperated engine.
In short, putting a supercharged head on a normally asperated engine will give you very bad acceleration and drivability, due to the increased combustion chamber size. The lower compression of the S/C engine's head on a normal engine will have bad idle, poor acceleration, and bad hesitation.
To tell the difference, you need both variants of cylinder head, and measure the cubic centimeters of the combustion chambers with a liquid. The one that holds more volume is the S/C head.
Thanks for choosing FixYa for assistance today. I hope that my answer helpd you out.
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