Someone can probably confirm but I thought all the 2.7s had auto hubs and it was only the 3.0 litre ones that did away with them.
Short of sticking one wheel on a set of rollers - which everyone has lying around don't they :lol: :lol: :lol: The only way I can suggest really is to find a clear quite bit of wet road somewhere and bring her up a few thousand revs and then dump the clutch in 1st, if she sits there spinning a wheel and stays fairly staight its not working if, the back kicks out quite a lot and you need to apply some opposite to keep her straight its working.
No seriously, just put one wheel on a bit of wet grass/mud somewhere and the other on tarmac/concrete and set off briskly, if the diffs working you should set off fairly well if not you'll know about it as you'll stay pretty still and start digging a whole, will work even better if you can find a place to do it on a hill.