Hi Cam,
Most US delivered Six 3's were low compression 8:1 motors with emission control, note the 2 black boxs behind the air compressor on the left hand side of the pic. These boxs control solonoids that cut fuel on a trailing throttle to reduce NOx. The 3d cam in the MFI pump is also different.
The result is a much less energetic 6.3.
Wait for a 9:1 comp car.