A document everyone should be aware of is the **broken link removed**. Other companies have similar reference manuals. This is a good place to check pitch and center-to-center pad spacing.
As Ian said, the pads can always be longer than the minimum distance - just be sure to extend outward from the center and don't change the internal gap.
I would keep the pads symmetric across the chip - don't make the pads on one side longer than on the other. This would make it harder to judge where the chip should be on the pads and if you're reflow soldering, weird things can happen if the pads are different sizes.