Have you ever considered a career in foot modeling Walter? You may get some offers after that post. I must say I was too distracted to notice the valve, but now that I see it, that's a great tool. Most Marklin boiler threads match one of the US fractional fine threads although I can't recall which one at the moment. I've never tried pulling out a dent but have always done it the hard way by opening up the boiler, but that's really difficult with many Marklins which have silver soldered flues.
That's very very clever Bruce.