I removed it tonight....
There should be a toll pin that locates the nut but this was missing....
A small easy out inserted and turned to grip resulted in extracting it from the casting....
I just need to make new nut then good as new.....

Update,
New nut made and in situ, works like charm.....

Dunno why I was worried about getting it out in the first place..

Although there is a roll pin adjacent to it to stop it rotating, and a screwed bush that stops it from coming out....( but that's missing too....!)
The rebuild continues....