If you are intending to operate this boiler in a public environment I suggest you contact
They can put you in touch with a local boiler tester who can test and issue certificates for your boiler. This will ensure your third party insurance is valid in the event of an incident. I would make contact before you attempt any re-threading repairs.
I have the same boiler and use at home to drive the ST beam engine I acquired at the same time. If I exhibit I run on compressed air.
Looks like it is cleaning up well.