I've finished the restoration of this engine. First off I decided to take apart the boiler, there was a dent in the faceplate of the boiler that needed some attention.
I used the contraption below to secure the boiler while desoldering the facepate:
On the image below you can see the facepate, I placed a matchstick on it to reveil the dent:
I was able to get the dent out with a special kind of hammer. While working on it, I also had to resolder the water lever plug tread, since that got loose. After resoldering it, it looked like this:
After the boiler was done, I had to work on the metal parts of the engine. I wanted to repaint the basepate and firebox, but for both I had to et special paint.
The firebox required crincle paint, which I found out VHT sells. For the baseplate I had paint mixed to a exact match.
The crincle paint wasn't much of a succes, it just didn't wrikle a lot. After all the painting was don, I was able to re-assemble it, the end result looked pretty nice: