[David Hodgson]

If the diff alignment is not spot on, an alignment shop can still set up the rear wheels with the Jag adjustments.

It is best practise to have the extended axis of the pinion and crankshaft in the same planes for the uni's to function correctly. So it is not critical if you are not spot on now.

Having said that, as the suspension raises and lowers, the angle of the of the hub's change in relation to the diff axle flanges, though this is only momentry.

A quick way of checking your rear alignment is way out(this works best with solid rear axles) is to roll the car straigh through wet pavement on to dry and check the tracking of the rear in relation to the fronts.