Help on shortening a Dana 60 truck housing

You don't need to plug in those measurements. Just hit "calculate" after entering data in the first three steps, and it'll populate those fields automatically. After plugging in Dana 60, stock Mopar pinion offset, and stock A-body width, it says "A" should be 20.49" and "B" should be 21.865".
Well there you go, just need to know how to do it. Thanks