It's written on the ID plate of the car. Located on the firewall, Eg. HG43 represents H233 diff 4.3 ratio. HH represents a rear H260 rear diff. Rare but does happen, have a look yourself and report back.
Just to clarify I am looking at a set of gu centres on ebay so no car and no id plate to check. I was under the impression that the 3.0 tds all had 4.3. Just seemed odd to me so thought I woukd check with the wiser ppl on here