As I had been waiting for a new drive shaft I thought I would have the diff out and have another look, so all stripped and cleaned I started experimenting with the shims.
I ended up with two shims on the pinion and none on the big gear wheel, which resulted in a very nice contact patch it's a little high on the tooth but both drive and over run patches look good, it turned out to be a bit of a trade off between contact patch and back lash.
The back lash is a little big but I can't detect and problems when driving.
Noise has been greatly reduced in both drive and overrun, when turning the diff by hand it no longer feels notchy as if the gears are bashing into each other, it's nice and smooth like it should be.
This might not be the same for everyone but it's worked for me and I'm very happy
