Thanks all.
The hood is held against the top cover by the usual Graflex bar arrangement, and I've separated that part. I have also removed the top cover.
The hood now looks like its attached to a frame thats screwed down, unfortunately the screw heads are inside the hood, which is difficult and awkward to deal with.
The bellows also look like they are held on the internal frame by screws in the inner sides of the internal frame.

Also, the bellows are not, it turns out, made on a tapered but straight form, but seem to be curved. Thats new one for me !

This is a $&*^%$(*@# system to work on !

To mount a 4x5 back I will have to reposition the groundglass higher by about an inch. That may prove interesting.