The good news Ash is it gives me an idea as to what a 400N Superdream might be worth so I will fix my budget accordingly. You are correct I'm in need of more homework, I am realistic enough to know it will be worth less than I spend on her, I'm unlikely to be able to ride or live long enough to get my money back. For me its all about the build with some red lines on cost.
For the first time I'm going to try to put a cap on my spending from the start, price up what needs doing before I spend any money for a planned 18-24 month project. The boxes of used parts might have some value to help with rebuild costs, or not.
There is a small oil leak at the front of the engine so the top of the engine at the very least will need to come off.
The one thing that is not going to suffer is the seat that has been replaced with a used one & comes with a complete new cover & strap ready for fitting. The base is said to be good so I will speak to some of the restorers that have been mentioned on here.
I have collected all the paperwork and a couple of boxes of used spares today so my first task will be to catalogue all the extra parts then identify them if it's not obvious. There is aso a small box of new parts in the deal. The bike itself is due to arrive sometime tommorow. I'll post some pictures up.