2006, TD42ti wagon with 285 tyres. I want to swap diffs from 3.9s to 4.1s. I don't want to fork out money for a 4.1 only to find it doesn't fit and I've done my dough. Can someone clearly tell me how I can recognise/ID a 4.1 diff that will fit straight into where my 3.9s came from before I buy it? I don't care how long winded your explanation is so long as it's helpful. Hoping someone can help, Deevo.