technicaly speaking there is no need for a caster angle on your rear wheels, this angle is set in to the front wheels to aid self centering of the steering, like on a shopping trolley wheel. unless your rear wheels are steered or damaged in some way there is not usually a way to adjust this angle.

The alignment angle called caster helps with steering wheel return.

A caster gauge is a tool used to measure the angle of a vehicle's steering axis in relation to vertical when viewed from the side. It is commonly used to determine and adjust the caster angle of the vehicle's front wheels, which affects steering stability and handling.

Yes, an aftermarket mustang caster plate will fit on your mk vii. it will give you a greater choice of caster angle, but not much more. If you are planning ten seconds in a quarter mile i would say go ahead. but if you are just cruising around town in a stock vehicle, there is not much of an advantage.

hope this helps

loose steering parts wheels out of balance caster align angle far out of spec (not likely if not in accident)