I think the cylinder walls are too thin to be stroked. I don't think there's any more displacement to be had from the 2ZZ.
The Trial Kit, which is the only kit that I know of so far, accomplishes the "stroking" by increasing the "stroke" by way of the Trial crank, not the bore. By my calculations the stroke is increased to about 95 mm as opposed to the stock 85 mm. That's a 1 cm difference, or 12% increase in stroke/cylinder which accounts for the 22% increase in hp!!! (220 hp up from 180 hp).