Really nice work there I must say!

I am very much impressed by your skills and workmanship

Then you touch on the subject of boiler. A thing that have crossed my mind as well, even though that is as far as it has come to date. Having looked through a couple of books on the subject, I have been thinking of saving up to buy a soldered boiler kit with test certificate and do the finishing bits myself, something like the GLR vertical semi-finished kit. That would eleiminate the sensitive part where much practice and tests is a must - something I do not have.
Then I would set it up so that I can change engine towards the same boiler and thus be able to run more than one engine according to my liking. The tricky part would of course be to define the interface between engine and boiler so that they can be made separately and still fit to each other.
Well, my 2 cents ...
BR
/Peter