I hope everyone appreciates this. Getting to this stage took at least 2 hours!
After yesterdays admission of error, I attacked the soldered joins making up the smokebox/boiler/firebox unit and reduced the parts to brass bits with blobs of solder on the edges. Mr Gas torch was very useful here as I could zap heat into the joints and shove scalpels into the3 metal to prise apart the components.
After this, re-assembly was simple-ish. Yes I had to file some of the solder blobs away with a coarse file. Others were melted and smeared around the metal so they didn't get in the way. I didn't burn my fingers and even remembered to shorten the boiler very slightly for a better fit. It's not pretty under there but since no-one will see, I don't care.
After cleaning up, the whitemetal bits started to find their way on, held in place with superglue. I reckoned I'd finished soldering until I spotted that the nuts to bolt the thing to the chassis haven't been fitted yet. Good job they are well away from the glued on bits!
Of course the sharp eyed will have spotted that the floor is still back to front. The difference between the two ends is the holes for sandboxes and I will hide these when I make up a new wooden floor.