Well, I did it. I laced in my replacement hub (which I had skimmed last week).
The job took the best part of 4 hours, most of which was taken up with stripping the old wheel and cleaning the parts up again. I re-used the stainless steel spokes and the rim.
To true the wheel I first refitted the old wheel to the bike, without the tyre. I then clamped a set square to my Raask rear sets and marked off where the rim edge was. This way the square whould show me that the hub was central in the wheel and the offset (as such) could be dialled in.
The wheel was built on a flat surface - i.e. the kitchen sideboard - which is why it was all cleaned up first! And then fitted to the bike for a final tweek. The building and trueing took an hour or so. The steps I took we as follws:
1. Get the hub central in the wheel.
2. Get the offset right.
3. Tighten up the spokes all round the wheel without disturbing the above. Keep spinning the wheel all the time.
I used a small spanner about 2 or 3 inches long. So as not to put too much torque on.
I then took the wheel down to my local tyre shop and they refitted the tyre and balanced the wheel yesterday. I told them I had built it and it was the first time I had done such a thing. They seem to be quite happy with it. Its now back on the bike and I have enough clearance on the swing arm.
I am feeling quite pleased.....

I will keep an eye on it and check it in a couple of thousand miles - when the old tyre will need replacing. Almost time for an MOT.
Here is a picture.