English axle diff rebuild, diff bearing pre-load.

I am rebuilding an english axle . The Ford manual talks about a spread on the bearing caps, i.e. a pre-load on the diff bearings. As this info is 30+ years old and seems to rely on the bearing caps moving apart, is there any other measurement that can be used to get the correct pre-load on the diff bearings? Just to clarify I am not talking about the pinion bearings.
 
thanks
 
Dave