We had to grind off a little bit from where the trailing arm meets the hub and some from the original brake caliper bracket. Then it is still a tight fit. Oh yes and the dust/stone guards have to come off or be cut up. Wish they would of told us this or even provided some instructions...
Here's the evidence:
DSC_2068 by edward guest, on Flickr
DSC_2069 by edward guest, on Flickr
DSC_2072 by edward guest, on Flickr
DSC_2074 by edward guest, on Flickr
If anyone wants to do it then note the pictures above, pain in the arse! But there are not many other options for us.
It adds 22mm diameter to the rear disc and so it is worth doing if you put some bigger brakes on the front, you get a better back to front braking balance.