What year car are you working on?

Track width is only part of the equation, a wide track car with a larger rear differential ( wider ) might have the same axle as a narrow track car with a smaller diff ( narrower. )

As an example, go to car-part dot com , look up a 97 C280 without traction control ( no ASR ) , it uses the same axle as a 87 - 95 E class.

You might be able to swap joints and reuse your axle shaft.