The stock engines were "off center", in that the cylinders are not precisely aligned with the crank throws. That means that the piston rods don't sit in the middle of the piston pin, but offset to one side or the other. Some of the Stage blocks were cast "on center" so that the crank throws are aligned with the cylinder bores, and the rods run in the center of the piston pin. To match the unique cylinder spacing, the heads and intakes had some dimensions changed, so that they are not interchangeable with the stock or the "off center" stage parts. I think there are pictures of the various different parts on the GnTTYpe.org web site, but it's down temporarily.
