Boiler flame fixed, and firedoor progress
The propane burner was fixed by RTFM. There I noted that the burner was intended to be run straight off the bottle with no regulator.
I replaced the jet with one of the original size, and connected the supply hose directly to the bottle without a regulator. Resulting in a beautiful clear blue flame. Which did not show up well on a photo so you will just have to take my word for that. I intend to experiment with slightly larger jet openings to fine tune it.
Then to finish the workshop session I made some fiddly little bits for the fire door. “Bling” as my friend John would characterise it.

You might notice the latch limiter, and the handles on the latch and the vent. M2 screws. All of those bits work well. Some finish filing still to be done.