Adjust the uppers back or the lowers forward, the lowers have provision for factory adjustment so I normally go with those as these are the ones they adjusted at the factory for caster and pinion angle. It will also lengthen the wheelbase rather than shorten it, of course it does depend how long you have the control arms, ideally you want to aim to have the wheel in the centre of the arch. To check the diff is straight measure the wheelbase on either side, so somewhere consistent on each rear wheel to a consistent spot on the front wheel. The front mounting points may not be 100%

Cheers
Steve