Quick 10MIN guide for BMW differentials 

Thanks! Hope you found it useful

Hey! Almost certain that if your engine spec is stock, you have a 188 diff in there. 210 came with the biggest engines like on the M5 models. You can also check the factory list when you decode your Vin-number to see if there are any mentions about your car´s diff options. Usually not, because 2.0 and such were most likely stock optioned.

The research that I did at the time were specialised for E30´s, although good to know about the variety

To my knowledge Z3 differentials swap to E30, swap output flanges and covers as needed. Depending on specific ratios and different models, I would still dig a bit in the old interwebs or compare pictures to be 100%