Okay, so, I had a go. There was no wobble, the barrel just wouldn't lock up and it seemed close. I took a tiny amount out of the barrel pivot, and then shaved the barrel shelf just a bit.
Now, I get closure, but not a "click". When it closes, I cannot open it pushing hard across my knee but the release mechanism isn't at its full height. And, (sorry no feeler gauges) at the top of the barrel face I have a gap as wide as a piece of household aluminium foil folded once and smoothed to completely compressed thickness, ie the width of two sheets of light household aluminium foil.
Based on previous experience, does this seem suitable - thereby allowing some "break in" once it starts shooting, or does it sound like I should shave the barrel shelf slightly more?