I think all of the ones with the tall carb flange (1"+) are for on-center, but I can't swear to it.
If you have a stock intake around, put a straight edge across the bottom of it at the center of a bolt hole; measure to the nearest bolt hole on the opposite side. Compare with your S2 intake. I have both around here but I'm too lazy to go dig things out and measure.
Thanks Kendall- i looked at a couple S2 intakes and i think you re correct on the height of the intake flange-the shorter ones are off center and taller ones on center.