My mechanic moved to SC for a job at the BMW factory. He left me some spares, but I am not totally sure what is what. In particular I have a rear diff from a 3 series, the only numbers I can make out on the housing are 1 210 321 , and 3 0703 83. Can anyone tell me what this will fit and possibly the ratio??? Also is there any way to check if it is limited slip?? anything will help. Thanks in advance.