Im thinking a Big Block Chevy maybe a 427 corvette motor, or a 500 ci Caddy motor.
The stock IQ motor is a Toyota Motor family number 1NR-FE.
The 1NR-FE engine I think is the most powerful in it's engine family.
The 2NR-FE & 3NR-FE are not as powerful as the engine that is already in it, the 1NR-FE
The NON-USA engine has slightly more power, I think it is about 100H.P. & 97.4 ft lbs torque.
The best thing to do is:
If someone could get an engine chip, to make the extra power, And remap the trans at the same time to remove the lag, Toyota tried to make the trans more like a convention shifting transmission by putting hesitation spots in acceleration(like it is shifting), they are not that noticeable, but they are there, to make it seem more like a conventional shifting 5 speed automatic trans. This slows down the car a little. The Trans Mapping might be done through the engine remapping.
It will be interesting to see what the after market comes out with.