I need to replace my rear differential case on my ford NAA. I found a doner casting. I understand that a paper gasket is needed to ensure proper preload for the differential bearings. Are the tolerances on the rear casting and trumpets close enough to be considered interchangeable or do I need to concern my self with the preload on the differential bearings? How would one check this if needed?

I understand that I will have to set the preload on outer bearing of the axle shafts. When both wheel turn the same too tight and add shims until one turns opposite.