I don't know the exact diff you're working on, I've only done the ones in Series 3s and 9/110 etc. In these the correct pinion height is etched onto the pinion face, and shims are available in 0.002 steps to get you to that exact figure.
Have you got the green official manual?
Edit to add. I'm puzzled that it's that far wrong - did you do the adjustment of preload etc?